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Introduction to decorative rhodium plating Slide 2 Consumer awareness for white gold and rhodium plating Slide 3 White gold alloys and rhodium plating Slide 4 Rhodium plating and its decorative applications Slide 5 Thickness specifications for rhodium plating Slide 7

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slide1

Introduction to decorative rhodium plating

Slide 2

Consumer awareness for white gold and rhodium plating

Slide 3

White gold alloys and rhodium plating

Slide 4

Rhodium plating and its decorative applications

Slide 5

Thickness specifications for rhodium plating

Slide 7

Reflective qualities of the “white” metals

Slide 8

Color shift from surface scratches on white gold alloys

Slide 6

Avoid the voids – Density requirements for rhodium plating

1

Decorative

Rhodium Plating

and its usage on white gold alloys

About the author

My name is Dave Vinson, director of Metal Arts Specialties. I have been involved with providing electroplated precious metal coatings since 1973.

We are one of the proud commercial sponsors on Finishing.com

They have been very

generous to provide us an opportunity to present this tutorial on rhodium plating and white gold to you.

Keep in mind that the electroplating of rhodium is a complex topic, not very easily explained without some simplification.

Slide index to this tutorial

There is a very good chance that this information will not answer every question you may have. Therefore, we invite you to further explore our web site www.artisanplating.com for more information about our new “rhodium ultra” plating process that is focused toward raising the standards for the decorative rhodium plating on white gold jewelry.

At the end of this tutorial, I have cited several excellent sources for individuals interested in additional research on rhodium and its related topics. There are also some interesting websites that explain nickel exposure and some of the key factors that lead to skin dermatitis.

The sources provided here offer some of the most objective information available and hopefully will provide useful ideas for additional inquiry. Be sure and check out the search engine and archives provided by www.finishing.com for additional information about real world issues with regard to white gold and rhodium plating. Thanks!

Slide 9

Common urban myths about rhodium plating

Slide 10

Rhodium plating- the most frequently asked questions

Slide 11

Rhodium plating- frequently asked questions, part 2

Slide 12

Plating specifications for decorative rhodium coatings

Slide 13

Key considerations for the rhodium plating on jewelry

Slide 14

Some physic, insights and pontifications

Slide 15

Bibliography and references

slide2

Consumer awareness for white gold and rhodium plating

2

The second issue needing to be addressed is the usage of nickel as a main alloy material in white gold. The focus is the sensitivity to nickel. Nickel alloys in white gold are creating skin allergies in a growing number of people This is real trouble for jewelry worn everyday. The problem is so bad that Europe has banned nickel in jewelry products! Often customers may not develop an allergy until after several years of ownership! By then the sentimental attachment to their jewelry does not allow them to easily replace it with a non-allergenic metal. Some customers are hoping that rhodium plating can eliminate the direct exposure to the white gold and delay or minimize their skin allergy. The industry is looking at the usage of non-nickel alloys for white gold. The good news is that more new “nickel free” alloys for white gold are now becoming more available.

As the popularity of white gold fashion jewelry increases, with it emerges two issues that affect today’s consumers. The first issue is the usage of rhodium plating as a top coat over white gold. The second issue is skin allergies caused from nickel alloys used in white gold jewelry to bleach it to a white color. Both issues are inter-related and have generated a huge amount of discussion among the trade and various consumer groups. It is clear to the casual observer that most first time owners of white gold are unaware of these issues and how it may affect them. Lets explore the first issue, the use of rhodium plating over their white gold to make it appear brighter. The coating is thin and as the rhodium wears away, the darker white gold is exposed. Many owners generally become angry when they realize that frequent re-plating will be needed. It is clear from the

In defense of your local jeweler

You may not realize it, but your local jeweler is an extremely talented business man! Not only does he or she need to understand the competitive aspect of running a small business, they must also be a highly creative and skilled craftsperson. Competency in setting diamonds, repairing watches, resizing rings, adjusting clocks, jewelry repair, polishing, the list goes on! As you can imagine the equipment and the people needed to provide support to the showroom sales team is no small thing. When a white gold ring is to be repaired or re-sized it will also need re-plating to conceal the weld joint line. Since most white gold sold in the U.S. today is rhodium plated, your jeweler has to be able to provide that skill.

From the authors perspective, your jeweler is an honest, conscientious and somewhat sentimental person who values happy customers. Sometimes there is “disconnect” between the customer and the sales team with regard to the usage of rhodium plating to enhance white gold jewelry. It has been the authors experience that full disclosure is generally provided to the customer. In reality, the excitement of the purchase will prevent the buyer from understanding or recalling the true implications of purchasing white gold (future re-plating). The best sales teams at a jewelry store will always make sure you understand what will be needed to keep your white gold jewelry looking great. Most will re-plate your white gold jewelry at no charge if it were to wear off too soon. So always give your jeweler a chance to assist you, they are the good guys!

In the U.S. nickel has been used as the main “bleaching” alloy in white gold for well over eighty

years. Nickel provides a good low cost method for making yellow gold appear white in color and

has good metallurgical and metal forming properties. The majority of white golds use nickel alloys.

numerous complaints and concerns being voiced by new owners that the usage of rhodium as a temporary coating is not being well received. Many complain that their jeweler did not adequately inform them of the rhodium plating. In some cases this may be true, in most cases the jewelers are very clear on this. However, despite full disclosure numerous owners are disappointed with the durability of their rhodium coating and are not happy about the trip to the jewelry store every six months to a year for re-plating. Rightfully, many newly engaged customers are concerned that their white gold ring prematurely looks dull and gray and they are not even married yet. Often they ask, how will their ring last a lifetime if this keeps happening? This is a fair question and deserves a fair and accurate answer by their

Jeweler and the industry trade groups as well.

Complicating these two issues is the large amount of inaccurate information being circulated among jewelry consumers. Some of it is too simplistic, most of it is just plain wrong. The task of today’s jeweler is to provide accurate information about nickel white gold. Full disclosure of the usage of rhodium both verbally and in writing at the time of sale must be common practice. In addition, the technical staffs that support the sales team need to update their rhodium plating capability to

meet the requirements of their white gold customers. This is by no means an easy task, as most jewelers are confident that their shop methods are already adequate. Often is heard, “Only a few people have these problems and therefore, the issue is no big deal” Clearly, this short sighted viewpoint is not shared or easily accepted by a majority of their customers.

slide3

White gold alloys and rhodium plating

Melting

temperature

3570.8 degrees F

Finish

appearance

Shiny

white/metallic

Surface hardness

when plated

800-1000

Hardness vickers

Corrosion

resistance

Best in class

Costs per troy ounce

$425-$2200

Trading range

Reflectivity

Reflect 78%-80%

of visible light

Typical plating

thickness

.05 microns to

2.5 microns

3

expensive progressive dies to form the final design contours (die striking). Lost wax casting enabled jewelers to create low volume and one of a kind jewelry designs that were more complex and unique than otherwise possible with die struck designs. The down side to white gold designs using the casting method is porosity within the design itself. Porosity is a series tiny voids that are present at the surface and through-out the cast white gold alloy. Jewelry that is created using the lost wax cast method is more difficult to plate with rhodium due to the presence of this porosity.

Today, nearly all nickel white gold whether cast, hand fabricated, or die struck uses rhodium plating to brighten its appearance. Die struck jewelry designs are still utilized on high volume jewelry such as wedding bands, class rings, and engagement settings. Most have simple design shapes which are required for die struck methods.

It is important to note that a jewelry item that is die struck provides a dense surface layer that is highly suitable for rhodium plating. This type of plated finish will last far longer than rhodium plated onto a custom cast white gold jewelry item.

Later on in this tutorial, a detailed explanation is provided for your reference.

From a electroplating perspective, providing a thick, pore free and durable coating of rhodium over white gold jewelry subjected to the normal high wear and chemical exposure is not easily achieved. The key word here is durability. It must meet the reasonable expectations of most owners of white gold jewelry.

In the next several slides, we will carefully explain the numerous factors that govern the successful plating of rhodium. We hope we can help dispel some of the myths, exaggerations, and belief based on bad physics that are prevalent among many consumers, and within the jewelry trade itself.

It is nearly impossible to continue a normal discussion on white gold without including rhodium plating. In fact the next several slides

are focused on the technical parameters of rhodium plating onto white gold alloys.

But first a little background information.

Since the early 1950’s the applications of decorative rhodium plating has grown steadily within the jewelry industry. Post war prosperity,

a shift in public tastes toward white gold, and

the availability of more suitable rhodium plating chemistries, have all contributed to this growth. Up until this time, palladium based white gold were quite expensive and were used on higher fashion jewelry. Due to costs, white gold alloys moved away from palladium and toward using nickel as its main “bleaching” alloy. In addition, nickel white gold had many technical benefits relative to fabrication of jewelry items that made its use attractive. Ease of casting, die forming, repair, and structural toughness endeared nickel white gold alloys to the jewelry trade and its manufacturers then. It remains popular today.

During this time frame most jewelers had not realized that some of the new cleaning chemistries being introduced into consumer household products readily attacked this alloy. Chlorine was one of the main ingredient in numerous “miracle” cleaners of the day. They soon discovered that nickel white gold alloys had a tendency to darken quickly when exposed to chlorine. As a result, the electroplating of rhodium began to gain wider usage as a “top coat”. Rhodium prevented the nickel white gold from discoloring and made the overall ring appear brighter in color due to greater reflectivity.

By the early 1960’s many gold jewelry items were created using a process called lost waxcasting. This method was used to replace a series of

Rhodium, its discovery and usages.

There is a key relationship between rhodium and white gold. But before we get into that, lets spend a moment to describe rhodium and its properties. From the Greek word “Rhodon” (rose), rhodium gets its name from the rose color appearance while it is in a liquid chemical state. It was discovered in 1803 by William Wollaston. Rhodium is a member of the platinum metals family, platinum palladium, osmium, ruthenium and iridium being the other metals in this group.

It is used industry wide in numerous applications as a coating to prevent corrosion and to increase mechanical wear when exposed to high temperatures. Rhodium will maintain a bright metallic white color under all normal atmospheric conditions at ordinary service temperatures.

In the last few years, there have been several innovative new improvements in the methods and

the bath chemistries for rhodium plating. Thick, bright and stress free coatings can be created to

replace the traditional flash coatings used today on white gold jewelry. Better physics, better results!

slide4

Rhodium plating and its decorative applications

4

“ The object of the present invention is to make

available to the plating industry and jewelry trade

the color and brilliance of rhodium by the

manufacture of a practical electroplating solution

by which the industry or trade may apply a finish,

or electroplate after the article is completely

manufactured and polished.

Among other attributes of rhodium which make

it highly desirable as a coating or plated on jewelry

are its color, which is silvery white, its resistance

to atmospheric oxidation. Its chemical inactivity,

therefore, causes it to be non-susceptible to

tarnishing” Thomas Shields, inventor 1934

In the beginning …….

The plating of rhodium began as early as 1891 but for many years remained only an academic curiosity. The plating of rhodium was also limited by the poor reliability of the chemistry itself and its high initial cost. In the early 1920’s, interest in rhodium grew due to its consideration as a reflective coating for incandescent automotive head lamps.

The practical methods for the plating of rhodium coatings received a big boost in the early 1930’s. Thomas Shields patented a stable plating chemistry that could be readily utilized by the jewelry industry. Shields primary intent was to provide a means for which metal items could be protected from tarnish and oxidation. This was quickly adopted by the merchants who sold sterling silver goods. As the popularity of rhodium began to grow the advent of world war II diverted its use as a military strategic metal. As a result, rhodium was not available again for commercial use until the late 1940’s. The extensive use of rhodium for plating fine silverware never caught on with consumers. However, it was largely due to the popularity of white gold jewelry that rhodium found its most popular applications. Today, rhodium plating is highly valued for its ability to conceal the gray color of white gold alloys.

“The chief purpose of this solution is to produce

a plate of rhodium on a highly polished article,

which will not detract any of the luster or polish

of the metal to be plated, while giving it a

protecting coat. Hence, after plating with the

above solution in the manner indicated, the

article plated will require no polishing after

the plating operation” Thomas Shields, inventor

slide5

Thickness guidelines for decorative rhodium coatings

one micron

one Mil.

5

Nickel allergy remediation,

extreme sensitivity to metals.

2.0 microns

What rhodium thickness am I getting?

performance coat

Micro-inches, microns, millionths of an inch, and mils, what’s are they talking about?

For most consumers the unit of measurement to describe electroplated coatings are new and strange to the ear. To make matters worse these unique sounding measurement terms are often used in error by many people in the jewelry trade themselves!

So lets look at the basic differences. The “micro-inch” is an English unit of measurement that is based on “millionths of an inch”. So when something is described as 100 micro inches, it is literally 100 millionths of an inch in thickness!

In contrast, a “micron” is a metric unit. Microns (millionths of a meter) are also used as a descriptive term for plated thickness, especially for functional and scientific coatings applications. It takes 2.5 microns to equal 100 micro-inches. As a point of reference a human hair is 100 microns in thickness, so we are talking about very thin coatings to begin with.

In the field of electroplating 2.5 microns is considered a robust coating for gold “vermeil” jewelry. For rhodium coatings in general, achieving 100 micro-inches (2.5 microns) of stress free thickness is not easily accomplished. In fact, the jewelry industry seldom, if at all, will plate rhodium in a thickness greater than 30- 40 micro-inches, (1.0 microns). Most decorative coatings range from .05 microns to .10 microns in thickness.

Referring to the chart to the right, here are some thickness recommendations that are achievable for rhodium when the correct chemistry, processes, and training are used.

Engagement settings, key rings,

wedding bands, watches, watch bands.

1.5 microns

Cuff bracelets, money clips, neck chains

medallions, medium wear fashion rings, buckles, silverware, writing instruments.

1.0 microns

functional coat

Light necklace chains, dog tags, pendants,

tennis bracelets, cigarette boxes, hollowware,

hair combs, lighter cases.

.50 microns

Rhodium thickness

should be increased

if there is constant

contact with skin

tissue. (I.e. wedding

bands, chains etc).

When properly

electroplated, high

wear items should

last for many years.

Bracelet charms, trophy items, jewelry findings.

.25 microns

top coat

Decorative baby rattles, picture frames, decorative items.

.10 microns

.05 microns

How thick?

Too thin, only temporary plating for cheap gift items.

flash coat

Unit of

measurement

one

micro-inch

.0254

microns

=

=

“Its has about 6 mils

of rhodium plating”

One millionths of

an inch

Through ignorance or

sloppiness, the term “mil”

is often used in error to

describe millionths of an

inch. 6 mils literally would

be 150 microns thick!

That is much too thick

for any plated coating.

=

=

One millionths

of a meter

39.37

micro-inches

Ref. 1.

=

=

One thousandths

of an inch

25.4

microns

1000 microns = 1 millimeter, 1250 microns = thickness of U.S. dime

A human hair follicle is about 100 microns in thickness

slide6

Avoid the voids – Density requirements for rhodium plating

6

Its what’s inside that counts!

Are you dense? Its not just thickness !

Sectional view of a plated rhodium layer 400 x

Not to confuse anybody, but it is not just the thickness of the plated layer which preserves the durability the rhodium coating.

In reality, most veteran metal finishers will tell you that the “density” of the plated deposit is as critical as the plated thickness!

While a plated layer of decorative rhodium may look bright to the casual observer, in reality the deposit itself is often filled with open cracks, voids, inclusions, and tramp metal contaminants (see fig 1). The bottom line is that the rhodium layer is less dense and much less protective than it could be be.

There are many factors that cause these undesirable features. Contamination of the plating bath, sloppiness by the technician, (pre-cleaning, pickling, rinsing), or wrong type of d.c. power supply; all contribute to some degree. In addition to this, if too much hydrogen (d.c over voltage) is created, the rhodium deposit itself will become too hard and brittle from the build-up internal stress. This stress can also cause macro cracking throughout the entire structure of the rhodium coating, especially in thick coatings.

Now bear in mind even with all of this going on, the rhodium plating will probably look bright and reflective to the naked eye! Unfortunately, the rhodium is no better than a temporary “topcoat”, and has little long term protective value.

Fortunately, proper plating methods and the availability of improved bath chemistry can eliminate inferior rhodium coatings.

When plated with the correct density and thickness, rhodium is an excellent protective coating!

Inclusions and pores diminish effectiveness of rhodium layer.

Stress crack

through entire

plated layer.

Contamination between

white gold and plated layer causes premature”wear off”

of bright rhodium coating.

D

A

H

H

D

A closer look at stress

White gold

Humans are not the only ones who can feel the negative effects of stress! Rhodium coatings also can be greatly impacted by their own version of stress too. To plate a durable layer of rhodium requires that the “lattice structure” of the plated layer be properly aligned. Think of a lattice structure as analogous to neatly stacked apples at your local fruit market. The apples represent the perfect alignment (in theory) of the rhodium atoms. During the plating process, bath impurities and especially hydrogen imbed themselves within the rhodium layer and cause structural misalignments of the atomic arrangement. Distortions of the lattice structure itself causes tensile stressing of the rhodium. The thicker the plated layer the higher the forces of this stress. This is bad because stress forces can cause the plated rhodium to peel away from the metal substrate. In addition, unless properly controlled

macro-cracks will appear through out the rhodium layer and will dramatically diminish its protective value.

Fig 1

Impurities in white

gold alloy casting.

A simple journey!

Any crack or breach in the rhodium coating

can create long term problems. Using these cracks, surface contaminants and chloride ions secreted by the skin travel down to the substrate. Metal oxides form and then travel back to the surface through the same cracks. Nickel ions in the white gold will be exposed to skin tissue and overtime may cause an allergic reaction.

slide7

Reflective qualities of the “white” metals

Rhodium plated white gold

reflects 80% of light waves

striking its surface

Rhodium plated layer

White gold

7

Short history of rhodium plating

Originally used as a “top coat” in the late 1930’s to prevent silver goods from tarnishing, the virtues of rhodium plating were later applied to jewelry to enhance and brighten white gold alloys. Prohibited from usage during world war II, rhodium plating began to re-emerge in the early 1950’s as a decorative coating for consumer products. Oddly enough, the usage

of rhodium plating was only to provide a pleasing “first impression” at the jewelry counter for white gold alloys. It was not intended as a permanent coating for jewelry due to the very thin plated layer (.05-.10 microns) relative to

the rigorous requirements of everyday usage.

Palladium white gold alloys generally were left

un-plated and were widely used in Europe on fine jewelry.

100% reflectivity under 4200k light source

A little reflection on brightness …

silver 98%

One of the attractions of rhodium plating is its ability to reflect light. Among the most patriotic usages for rhodium coatings was its application as a specular coating for searchlight reflectors during world war II.

Taking advantage of rhodium’s ability to remain reflective even when exposed to high temperatures, the hot carbon element in search lights had little effect on the rhodium layer. The bowl like shape of the search light reflector was filled with a rhodium plating electrolyte and charged with a d.c. current. This allowed technicians to plate rhodium into the extremely large surface area of the reflector itself, and to simplify the entire manufacturing process. After world war II rhodium once again was available for commercial applications. With more the reliable plating chemistries, the jewelry industry soon re-discovered the virtues of bright rhodium. And it is no wonder that rhodium continues to remain the coating of choice for fashion jewelry. As a reference point, highly polished platinum jewelry reflects about 65% of the light striking it. White gold is a little better, reflecting 68% of light rays. Palladium is a little less reflective at 62%. With the exception of silver (98%)and polished aluminum (90%), rhodium is best in class for reflecting light rays.

rhodium 80%

white gold 68%

platinum 65%

palladium 62%

% Reflectivity of “white” metal finishes

Of all the platinum group metals only rhodium can claim the title of most reflective “white” metal. Only silver and polished aluminum are brighter. Neither of course will stay bright and reflective as rhodium coatings once exposed to contaminants found in normal everyday environmental conditions.

Did you know?

When full spectrum light rays strike a bright metallic

surface some of those rays are absorbed by the

metal itself. The more the light rays reflect upward,

the brighter the metal will appear to the observer.

Like crinkled tin foil, scratched surfaces scatter light

rays and the metal will appear dull and hazy.

slide8

Color shift from surface scratches on white gold alloys

8

My white gold ring looks yellowish!

Scratches on white gold jewelry surfaces

Once a white gold ring has lost its decorative coating of rhodium through everyday wear, it will begin to show surface scratches more readily. Minute scratches impart a dull appearance to a metal’s surface. For severely scratched jewelry the naturally pale yellow-gray color of white gold will become much more noticeable, especially under warm incandescent light sources. Most owners of white gold are somewhat surprised that their bright white gold now looks dull and yellow. In addition, as time progresses, exposure to chloride normally present in many household chemicals and skin perspiration will discolor the exposed white gold alloy to a darker gray-yellow color. Highly polished white gold minimizes the perception of the yellow gold atoms at the surface. In addition, the use of a thick, pore free layer of rhodium plating over the white gold ensures that a bright reflective surface preserves the beauty of your jewelry item.

Yellow gold is alloyed with nickel or palladium to “bleach” the gold to a white color. The alloy of choice for the U.S jewelry industry is nickel. Nickel is used as a whitener and is slightly yellow-gray in appearance. Even when highly polished, white gold alloys are less reflective to light waves than most people realize. In addition, once the polished surface is scratched or abraded from normal wear, the diffusive light rays being reflected from the white gold will appear less white in color. Depending on the type of light source and the angle of observation, the light waves being reflected from the scratched surface of the white gold will allow the casual observer to notice a yellowish tint along the surface of the white gold.

This is a natural outcome of light rays reflecting the color of the yellow gold atoms at a slightly different speed than the atoms of the nickel alloy material. See fig1

Normally the yellow “tint” of white gold would not be noticed if the surface remains highly polished. Of course that is unlikely for most everyday jewelry items such as wedding bands and engagement settings.

For several years, most white gold jewelry sold in the U.S have temporarily concealed this tint shift by plating the item with a bright rhodium layer. It is no wonder, plated rhodium is highly reflective, scratch resistant and impervious to most household chemicals. Unfortunately, most rhodium coatings used on commercial white gold jewelry are much too thin to last more than several months.

Incoming light rays

Reflected light rays from gold atoms

moving at different speed than nickel

Reflected light rays from nickel atoms

Ni

Ni

Ni

Au

Au

Au

Ni

Ni

Au

Au

Ni

Au

Au

Ni

Ni

Au

Au

Ni

Ni

Au

Au

Ni

Fig. 1

Conceptual model illustrating the different

specular qualities of gold and nickel atoms

reflected from a scratched surface on a typical

white gold alloy.

slide9

Common “urban myths” about rhodium plating

Myth # 2

Rhodium is a protective coating and will last for years, so don’t worry…...

Often oversold as a protective coating, decorative rhodium plating is regarded by its

inventor (Thomas Shields) as only a “top coat” not a suit of armor! Rhodium coatings in

greater than 60 micro-inches are excellent performance coatings and can last for years.

Myth # 3

A plating of rhodium over jewelry can easily eliminate your nickel allergies……

Not true, most rhodium coatings are macro-crack from being stressed during the plating

process. The coating must be crack free, and relatively thick to provide a “prophylactic”

enclosure to ensure that nickel leeching from the white gold does not come in skin contact.

I am sorry, but your rhodium wore off because of your body chemistry…….

Myth # 4

This is the cruelest myth. While the level of skin perspiration varies individually,

durability of the rhodium has more to do with its thickness and density of the plating.

Excess sodium chloride from the skin is not the root cause of the rhodium wearing off.

Rhodium is easily plated on any type of jewelry, wait here a minute…..

Myth # 5

Now this ought to tell you something about the quality of the rhodium plating you are

about to receive! When done correctly, re-plating will take more than a few minutes

especially if the plating area is staffed by a qualified goldsmith.

All our white gold is rhodium plated, I am sure we mentioned that to you……

Myth # 6

This is not a total myth. The higher quality jewelry stores will fully disclose the fact that

your white gold has been plated with rhodium. In many cases there will be actual signage

posted in the showcases.This does not mean that you the customer hears the message!

Myth # 7

You must be rough on your jewelry because rhodium does not scratch easily…

Rhodium plating is tough and hard, however that does not mean that it is scratch proof.

While nearly as scratch resistant as chrome, it will over time be subject to small abrasive

marks from everyday wear. It usually wears off before it has a chance to get scratched.

9

Its not what you don’t know that gets you in trouble, its what you do know that is simply wrong!

Mark Twain, American humorist

The truth will set you free, but first …

Now there are so many misconceptions that have evolved with regard to rhodium that it is impossible to discuss them all. So we will list the top seven “urban myths” that we hear

all too often from our customers.

But lets take a moment and understand the context of some of these myths and the reasons for their origins and usages.

Most rhodium coatings are considered to be “decorative”. They are applied to jewelry items made of white gold or silver. They are used to enhance surface appearance by brightening the reflective qualities of the jewelry itself. They are always used to conceal the repair area on white gold rings that have been resized for a new customer.

Silver chains, bracelets, and earrings are prime candidates for rhodium coatings and help prevent tarnishing from exposure to skin perspiration. Over the years, especially with the popularity of white gold jewelry, the expectations for decorative rhodium coatings have been grossly oversold to the public and within the jewelry industry itself! As they are typically plated today, rhodium coatings are too thin. This is true especially for coatings applied after minor jewelry repairs have been completed. The dubious plating methods

(i.e. pen plating) and chemistries (often contaminated) are not suitable for good quality rhodium coatings. The good news is that there are better methods and improved rhodium chemistries that could be adopted by the industry. Until this happens “urban myths” with regard to rhodium, white gold, and nickel allergies will keep on propagating within the public sector for many more years.

Myth # 1

Rhodium is so expensive, that is why it is plated is so thin…..

This is a popular statement often used to explain why rhodium plating is typically so thin

on commercial jewelry. Even when rhodium was over $2100 per ounce the actual material

costs used on a wedding ring with 10-20 micro-inches of rhodium was less than $10!

slide10

Rhodium plating – the most frequently asked questions

I’m mad, I was not aware that my jewelry was plated! Is it illegal to use rhodium plating over white gold jewelry and not advise the buyer about it?

No, it is not illegal to sell rhodium plated white gold without disclosing it to the customer. The best quality jewelry stores will always tell you. Some will even post small consumer signage within their display case. Often the customer does not hear the sales person’s disclosure due to the excitement of the moment.

After years of wear my mother’s white gold wedding band still looks great.

Why didn't hers need constant re-plating like mine has? I am real tired of this.

Your mothers white gold ring probably used palladium as its only whitening alloy instead of the more common

nickel used as an alloy today. Palladium white gold is chemically stable and remains a pleasing warm “gray white” and does not require rhodium plating to remain attractive or to resist discoloration from chemical exposure.

A few weeks ago I had my ring re-sized and the back of the band has developed small spots on the surface of the white gold, what is going on here?

There was a very good chance that the rhodium plating bath was contaminated with some other metal such as silver or iron. They were co-deposited with the rhodium. As they oxide, tiny spots show up on the plated surface.

The plating on the ring needs to be removed and re-plated onto a clean surface using a fresh plating bath.

I keep having to have my ring re-plated with rhodium about every six months, what can I do to have it last longer?

You need to have it plated with an adequate layer of rhodium. A minimum 30-40 micro-inches of uniform rhodium plating would provide excellent durability and would help eliminate so many frequent trips to the jewelry store.

Some stores will send their jewelry items out to specialty plating shops who can provide the heavier coatings.

10

The truth has many meanings

In this section we have attempted to provide a brief sampling of the most frequently asked questions that are often made by the public. We have tried to make each answer as succinct as possible, however, some answers are more complicated than others. Each answer may have other possible explanations that are beyond the scope of this tutorial. Unfortunately, for the technical purist, the answers provided here may not be as complete or as precise as we would like. Bear in mind that our real focus here is to assist those laypersons new to this subject.

I want to have a signet ring plated,

will rhodium plating conceal or obscure the fine details on engraved areas or hallmarks on the ring itself?

No, the plated layer while thick enough to provide a bright finish is quite thin. Even 100 micro-inches of rhodium will not conceal surface details, including scratches, engravings, and hallmarks. Sometimes during the polishing

process a zealous polisher will buff out the details and diminish the overall aesthetics of the piece.

I just recently replaced my nickel based white gold ring with a new palladium white gold ring and yet I am still getting a skin rash, what is going on here?

It would appear that your new ring also contains nickel. It is quite common to combine nickel with palladium as a bleaching agent for white gold. In general, a good balance is achieved between color and workability of the metal.

Be aware, just because it contains palladium does not mean that it does not contain a nickel alloy!

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Rhodium plating – the most frequently asked questions, part 2

I am in the doghouse! The plating on my fiancé's new engagement ring has worn off. Its only been 4 months, why did it wear off so soon?

If the ring was re-sized than probably the repair area was not properly cleaned prior to re-plating or there just

was not a thick enough layer of rhodium applied for adequate long term wear life. If the ring was created from a casting and not die struck, there could be porosity in the setting that caused the rhodium to wear off too soon.

I have developed a skin rash from my white gold ring! Would plating it with rhodium be an option for preventing this annoying rash from occurring?

This is a tough question. If you apply a thick layer of dense, pore free rhodium plating over the entire contact surface of the ring, including the inside contours, than yes, nickel rashes can be virtually eliminated. Just bear in

mind that any breach in the rhodium layer can cause re-exposure to the nickel in your white gold.

11

I don’t get it, my jewelry was expensive! Why is it that my jeweler won’t provide a guarantee in writing for my rhodium plated white gold ring?

Probably because of the numerous factors that determine the durability of the plating. These variables include, thickness of the rhodium, is the jewelry cast or die struck, exposure to chlorine from hot tubs, cleaning chemicals, and occupational contact with hard surfaces; all play a role in the durability of the rhodium plated jewelry.

I was told that the reason my rhodium

wore off my bracelet so quickly is due

to the perfume I wear. Is there any truth to this?

There is no doubt that exposure to chemicals can play a role in the diminished life of rhodium plating. Having said that there is much that can be done to minimize the effects of incidental contact with perfumes, soaps and

chlorine. Its starts with a thick, pore free, layer of rhodium applied over a clean surface using the correct methods.

I want to have a yellow gold chain

bracelet re-plated, how thick should the rhodium be and how long can I expect it to last?

Chains have to survive in an environment of perspiration, cologne, and constant soft abrasion of the links itching together as part of normal movement of the human body. Worn 24/7, they present one of the most significant challenges for a plated coating. You need at least 40 micro-inches of uniform rhodium; durability is 1-3 years.

I have had several silver jewelry items

tarnish slightly despite being plated

with rhodium, why did that happen?

The rhodium layer is probably too thin! The discoloring is due to the corrosive oxides that are "rising" through the microscopic pores within the rhodium's surface. This type of surface tarnish will eventually appear "yellowish” bright to the observer and is commonly found on decorative items such as jewelry chains and bracelets.

I am confused, what are the jewelry industry standards for decorative rhodium plated finishes?

For decorative coatings, there are no formal standards for the thickness of rhodium plating. There are some recommendations depending on the type of item to be plated. However, none reflect the technical inroads made recently by the electronics industry that produce dense, bright, pore free coatings. The jewelry industry is behind.

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Plating specifications for decorative rhodium coatings

12

Sometimes hot tubs are not cool!

Sorry to spoil your fun but the chlorine in your hot tub can have severe adverse effects on the life of your jewelry. When exposed to chlorine, the alloy material such as copper, silver, and nickel in your gold jewelry will be chemically attacked and will slowly dissolve! Discoloration of the metal followed by small stress cracks appearing in its surface indicate the weakening effects from chlorine exposure. Try to avoid wearing jewelry items into the pool or hot tub. Of course you will want to hire a cleaning service so as not to expose your jewelry to chlorine which is very common in most household cleaners. Right!

Its really about the fundamentals

There are no trade secrets to achieving quality rhodium coatings. Most of the real challenge lies in utilizing sound methods combined with the right plating chemistry.

Chiefly among the factors is cleanliness of the item that is to be re-plated. This can not be underestimated, often it is! Without a pristine almost “surgically clean” layer of metal, the rhodium plating will not adhere very well or last very long. In many cases surface oxides from the repair process and polishing contaminants remain imbedded in the outer atomic layer of the jewelry. They must be removed prior to the plating process. Often they are not! Sometimes soldering flux residues or grit material from the sanding process will cause small pin holes or voids in the plated surface. They are very small and can only be seen under a 10x magnifying loop. Over time these voids will visibly manifest themselves as brown spots, and surface specks within the otherwise bright rhodium layer. In some instances pre-existing porosity in the white gold metal casting will prevent the plating of rhodium in these local areas. This will substantially negate the protective benefits of the rhodium layer. However, this can be easily remedied by using a special “pre-coating” process designed to bridge and fill these tiny pores prior to the final rhodium coating. The final and often overlooked issue is contaminated rhodium plating baths. Rhodium chemistry is highly acidic and is easily picks up ”tramp” metals (copper, silver,iron from rouge dust). This will reduce the reflective brightness and will also cause hazy rhodium coatings.

The old rhodium coating shall be removed prior to repair and re-plating.

Spec # 1

Often overlooked as a crucial step toward achieving good quality rhodium coatings.

Old layers of rhodium often form a passive layer that resists adequate adhesion of the

new layer of bright rhodium. It is vital that this old layer be removed prior to re-plating.

The rhodium coating shall be only applied to clean and active surfaces.

Spec # 2

The biggest error often made is the lack of adequate cleaning of the jewelry surface prior

to re-plating. The surface must be pristine and chemically activated in order for the

rhodium to adhere. Contaminated rhodium baths will cause dull hazy rhodium deposits.

The rhodium coating shall be of adequate thickness.

Spec # 3

Lets face it most decorative rhodium plating are much too thin. Having measured many

rhodium coatings it is rare to find a plated thickness greater than 10-15 micro-inches.

Rhodium coatings must be at least 40-60 micro-inches for high wear jewelry items.

The rhodium coating shall have adequate density and free of voids.

Spec # 4

Density of the rhodium coating ultimately determines the level of protection and

actual durability of plated item. A dense, void free rhodium layer can more than double the

expected wear life of a typical plated white gold jewelry item.

The rhodium coating shall be free from macro-cracks.

Spec # 5

Thick rhodium coatings are useless if macro-cracks are prevalent within the plated layer.

Stressed rhodium deposits caused by contaminated baths, improper plating chemistry

and poor bench methods will provide access for perspiration to attacked the plated item.

The rhodium coating shall be uniform in thickness on all surface areas.

Spec # 6

Just because it looks bright and shiny is no indication of the actual uniformity of the

rhodium layer. The rhodium coating often is thinner on the inside regions

and hard to reach areas on an item of jewelry (I.e. inside surface of wedding band).

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Key considerations for the rhodium plating of jewelry

A key area where perfume,

hand cream, and dried soaps

accumulate. Their chemistry

can slowly attack the nickel

in the white gold alloy.

Another recessed area that

typically does not receive adequate thickness of plated rhodium.

13

Often one of the first plated

areas of a ring that fails are

the tight junction points. Low

current density sometimes

does not allow adequate deposition of the rhodium layer.

The constant rubbing against skin tissue will cause the plating in this area to be removed first. This area has higher wear than does the more exposed regions around the diamond setting itself!

In the final analysis, it’s the results!

There are several process and chemical parameters that must be observed when plating rhodium coatings. The complexity and description is beyond the scope of this tutorial. However, lets talk about the desired results relative to decorative plating of jewelry. We will use a rhodium plated, nickel alloy white gold engagement ring as our example. A rhodium coating must be reasonably thick and uniform on the entire contour of the ring itself. This includes all surfaces on the inside dimensions of the band itself (Fig 1). Included in this, are the metal areas under the small diamonds themselves. Often the typical plating process for rhodium will not allow for adequate thickness or deposition in these areas (Fig 2). Ironically, this is the most critical area for good long term performance of the plated coating as this region is in intimate contact with skin tissue all the time. When skin perspiration is present, the chloride ion evolved from body chemistry will begin to weep through any cracks in the thin rhodium coating (assuming there is arhodiumcoating there). At this point, the nickel atoms in the white gold will slowly be attacked by the chloride itself. The severity will depend on the individual’s body chemistry, and exposure to other common household chemicals. For the more visible areas of the ring (Fig 3), brightness and scratch resistance are the main reasons for the rhodium layer. Again, a robust layer of pore free rhodium is needed. Plated rhodium is highly resistant to incidental scratching. However no plated coating is totally scratch proof, including rhodium!

Fig1.

This is a high contact area and often will wear off first.

Tiny scratches will start to

make the diamond look dull.

Fig 2.

Fig 3.

Sensitive to Nickel?

Thin decorative rhodium

coatings were not intended

to protect the wearer from

exposure to nickel. The plating

must be thick, and pore free.

If the rhodium does not totally

cover the white gold, no viable

protection is possible. A tiny

breach anywhere in the

rhodium will allow chloride

ions from the skin to start the

reaction process to the nickel.

Frequently the starting point for

corrosion attack by chloride ions

secreted from skin perspiration.

Corrosion process is accelerated by too much time in the chlorine environments (I.e.hot tubs).

This location on the inside of

the band is often one of the first

areas to wear off. High incidental contact at back edges of the ring

quickens the wear off process.

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Some physics, insights and pontifications

14

A platinum remedy

Rhodium is in general

very scratch resistant, equal in hardness to chrome. Did you know that platinum plating can also be almost as tough as rhodium plating?

For those of you who are contemplating a new platinum ring but told it was too soft; you could have the new ring plated with a layer of platinum. The color is identical to the platinum metal because it is platinum! The difference is that this new plated layer is eight times harder and more scratch resistant than the un-plated ring would be. This method allows the softer platinum rings to wear much better and the scratch resistance easily rivals that of rhodium plated rings.

Sweating the details

Did you know that skin tissue

emits sodium chloride as the

main ingredient in sweat?

Chloride ions combined with

soaps, perfumes and oils all

play a key role in attacking

the metal in your jewelry.

The plating on your jewelry

needs be thick and pore free

to keep the metal “sealed”

from these substances. Any

breach in the plated coating

will allow the perspiration to

react to the metal and form

oxides. On occasion, some

of these oxides may cause

irritation of the skin tissue.

All nickel based white gold

jewelry are vulnerable to

chemical attack from chlorine.

Only the best surface survives: When selecting an engagement setting made from white gold, bear in mind that it is generally plated with rhodium. For best long term wear, always select a design that has been “die struck” instead of one that was created using the “lost wax cast” method. The die struck

design has a structure that is dense and pore free. The atoms of this type of design have been compressed together tightly leaving no surface voids. This design will provide an excellent surface to apply a thick, crack free, layer of durable rhodium. All things being equal in the plating process, rhodium applied over this type of surface will last significantly longer than one plated over a design created from a lost wax casting.

Oldie but goodie: Palladium based white gold made during the 1930’s

still offer a bright durable surface that is superior to today’s nickel based white gold alloys. In addition, many of these rings were die struck rather than cast. Numerous white gold heirloom pieces survive today looking as attractive

as the day they were purchased; without the use of rhodium plating too!

When possible select a white gold design that uses palladium as its sole alloy.

Pens aren’t for plating: Many jewelry stores use a small plating pen to

deposit a layer of rhodium after a minor repair. For white gold rings this

process does not provide a thick enough layer of rhodium to survive the

rigors of day to day exposure to chemicals. It doesn’t help either when the

surface of the ring is not adequately cleaned. It may quick and easy for the

jeweler but it is bad for customer satisfaction with regard to white gold rings.

A tough neighborhood

The traditional ring finger for your wedding band is located on one of the highest impact areas of your body. Frequent contact with door handles, tools, instruments, computers, eating utensils and countless other objects all provide numerous tiny impacts to your jewelry everyday! In fact your ring probably sees more incidental contact than the windshield on your car! It is no wonder that jewelry items become scratched and worn. Depending on your wear habits, you should expect to have your rings re-polished or re-plated periodically.

The physics of porosity: Many custom designed jewelry items are castings made in white gold.

All too often the casting itself is filled with tiny voids and pores. If these tiny pores are numerous

and are present at the rings surface, it is virtually impossible to seal the white gold with a layer of

plated rhodium. The plating process requires that a d.c. current of electricity pass along the surface

layer of the ring. The surface gaps created by the pores prevent the d.c current from depositing the

rhodium locally. This leaves the white gold unprotected at the “pore sites”. Over time a galvanic

corrosion will start at these pore sites and small spots from the base metal will become visible. The adhesion of the rhodium plating is the weakest in those regions where porosity is the greatest and

as a result it will wear off quicker.

slide15

Bibliography and references

15

Technical references for white gold and nickel allergies

Jerry Bowers - “Working with Palladium white gold” white paper, 1999

Hoover and Strong Company, Richmond, Virginia

Useful reference for palladium white gold alloys and their characteristics.

Some final thoughts and summary

Helpful web sites

As mentioned at the introduction of this

tutorial, there is a large amount of data on white gold, rhodium plating and nickel allergies. Due to legislation to remove nickel from consumer products, the European jewelry trade is far ahead of the unregulated U.S. markets. Most of the scientific information available for additional evaluation will be from sources outside of the U.S. With regard to rhodium plating itself, the methods and chemistry being utilized in Europe are the same as used by the jewelry trade in the U.S. Clearly, both Europe and the U.S. jewelry trade will need to update their rhodium plating processes.

www.gold.org

Fred Klotz - “Do chemicals attack your gold?” white paper, 1995

Hoover and Strong Company, Richmond, Virginia

Descriptions of chemicals and their corrosive impact on different gold alloys.

Home site for the World Gold Council. Good articles on

white gold alloys and nickel

skin allergies.

Andrew McDonaugh - “Nickel Sensitivity” British Journal of Dermatology

Clear explanations regarding nickel sensitivity for the layperson.

www.finishing.com

Peter Rotheram - “Meeting the Demands of International Legislation” DevelopmentDirector - Cookson Precious Metals, Birmingham, England

Good explanations regarding white gold, allergies and nickel free gold alloys.

Extensive archives on all things related to plating. Be sure to search their archives on rhodium and white gold.

Roy Rushforth - “Don’t let nickel get under your skin- the European experience” FormerDirector - The Assay office, Birmingham England

Excellent source for understanding nickel allergies relative to skin dermatitis.

www.about.com

Excellent search engine for basic information about nickel, jewelry, rhodium and all things related to metal.

Annoyed at your Jeweler?

share your concerns

Jewelers

vigilance committee

www.jvclegal.org

www.hooverandstrong.com

Technical References for rhodium

Expert information on white

gold alloys and their use in

in the manufacturing of

jewelry designs. Fine site!

S. Burling, D. Markey - Bright White Rhodium Plating of Decorative Coatings,AESF SUR/FIN 2000

William Blum, George Hogaboom - Principles of Electroplating and Electroforming, McGraw-Hill ISBN 07-006179-3

Y.S. Fung, W. S. Miu - Heavy Electro-deposition of Rhodium by Pulsed current, Tech Conf. AES 72nd Session

www.johnsonmatthey.com

Worlds largest source for

Platinum group metals and their compounds. Makers of rhodium plating chemistries.

F.Joly, J. Leidie, - Comptes Rendues, vol. 112 (1891)

J.B. Mohler - Electroplating and Related Processes, Chemical Publishing Company, NY

D.J. Morrissey - Overview of Rhodium Plating, Plating and Surface Finishing, 2004

www.unitedpmr.com

Derek Pletcher, Rosa Urbana - Electro-deposition of Rhodium,Journal of Electro-analytical Chemistry, 1997

One of the best sites for data on white gold, nickel, and their

relationship to rhodium plating methods. Nice people too!

F. H. Reid - Practical Aspects of Heavy Rhodium plating, Trans. Inst. Metal Finishing, Volume 33

W. H. Safranek - Properties of Electroplated Metals and Alloys, 2nd edition 1986 AESF

D. D. Vinson – Decorative rhodium plating for the 21st Century, new methods and chemistry,draftwhite paper, 2004

www.artisanplating.com

One of America’s premier sites for precious metal plating services. Providers of high quality rhodium plating.

U.S. Patent References for rhodium:

U.S. 1949131 (1934)

U.S. 2895889 (1959)

U.S. 3902978 (1975)

U.S. 4789437 (1989)

U.S. 3528895 (1970)

U.S. 4285784 (1981)

U.S. 5976341 (1999)

U.S. 2093406 (1937)

Photo credits: All photos taken using a Nikon Cool Pix 4500

with Cloud Dome,graphics touch-up with Adobe Photo Shop