copyright 2004 metal arts specialties page - the practical methods for the plating of rhodium...

Copyright 2004 Metal Arts Specialties www.artisanplating.com

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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.

In the beginning …….

Rhodium plating and its decorative applications

“The chief purpose of this solution is to producea plate of rhodium on a highly polished article,which will not detract any of the luster or polishof the metal to be plated, while giving it aprotecting coat. Hence, after plating with theabove solution in the manner indicated, thearticle plated will require no polishing after the plating operation” Thomas Shields, inventor

“ The object of the present invention is to makeavailable to the plating industry and jewelry tradethe color and brilliance of rhodium by the manufacture of a practical electroplating solutionby 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 jewelryare its color, which is silvery white, its resistanceto atmospheric oxidation. Its chemical inactivity,therefore, causes it to be non-susceptible to tarnishing” Thomas Shields, inventor 1934

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.


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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.

What rhodium thickness am I getting?

.05 microns

.10 microns

.25 microns

.50 microns

1.0 microns

1.5 microns

2.0 microns

Engagement settings, key rings,wedding bands, watches, watch bands.

Nickel allergy remediation,extreme sensitivity to metals.

Cuff bracelets, money clips, neck chainsmedallions, medium wear fashion rings, buckles, silverware, writing instruments.

Light necklace chains, dog tags, pendants,tennis bracelets, cigarette boxes, hollowware,hair combs, lighter cases.

Decorative baby rattles, picture frames, decorative items.

Too thin, only temporary plating for cheap gift items.

Bracelet charms, trophy items, jewelry findings.

How thick?

Unit of measurement

onemicro-inch

one Mil.

one micron

One millionths of an inch

One millionths of a meter

One thousandths of an inch

.0254microns

39.37 micro-inches

25.4microns

==

=

==

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

A human hair follicle is about 100 microns in thickness

Rhodium thicknessshould be increased if there is constantcontact with skin tissue. (I.e. weddingbands, chains etc).When properly electroplated, high wear items should last for many years.

Ref. 1.

“Its has about 6 mils of rhodium plating”

Through ignorance orsloppiness, the term “mil” is often used in error to describe millionths of an inch. 6 mils literally wouldbe 150 microns thick!That is much too thickfor any plated coating.

flash coat

top coat

functional coat

performance coat

Thickness guidelines for decorative rhodium coatings


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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!

Are you dense? Its not just thickness !

White goldHumans 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.

A closer look at stress

Contamination between white gold and plated layer causes premature”wear off”of bright rhodium coating.

Inclusions and pores diminish effectiveness

of rhodium layer.

Stress crackthrough entireplated layer.

Impurities in white gold alloy casting.

Its what’s inside that counts!Sectional view of a plated rhodium layer 400 x

A simple journey!

Fig 1

Any crack or breach in the rhodium coatingcan 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.

Avoid the voids – Density requirements for rhodium plating


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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.

A little reflection on brightness …

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.

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.

Did you know?

rhodium 80%

silver 98%

white gold 68%platinum 65%

palladium 62%

% Reflectivity of “white” metal finishes

100% reflectivity under 4200k light sourceShort history of rhodium platingOriginally 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 tothe rigorous requirements of everyday usage. Palladium white gold alloys generally were left un-plated and were widely used in Europe on fine jewelry.

Rhodium plated white goldreflects 80% of light wavesstriking its surface

Rhodium plated layer

White gold

Reflective qualities of the “white” metals


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Scratches on white gold jewelry surfacesOnce 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.

Fig. 1Conceptual model illustrating the differentspecular qualities of gold and nickel atomsreflected from a scratched surface on a typicalwhite gold alloy.

Au Ni Ni Au Au Au Ni

Au Ni Ni AuAu AuNi

Ni Au Au AuNi Ni

Ni

Reflected light rays from nickel atoms

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 fig1Normally 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.

My white gold ring looks yellowish!

Ni

Reflected light rays from gold atomsmoving at different speed than nickel

Incoming light rays

Color shift from surface scratches on white gold alloys8


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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 hearall 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.

The truth will set you free, but first …

Rhodium is so expensive, that is why it is plated is so thin…..Myth # 1

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

Rhodium is a protective coating and will last for years, so don’t worry…... Myth # 2

Often oversold as a protective coating, decorative rhodium plating is regarded by itsinventor (Thomas Shields) as only a “top coat” not a suit of armor! Rhodium coatings ingreater than 60 micro-inches are excellent performance coatings and can last for years.

A plating of rhodium over jewelry can easily eliminate your nickel allergies……Myth # 3

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

Myth # 6 All our white gold is rhodium plated, I am sure we mentioned that to you……

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

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

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

Common “urban myths” about rhodium plating


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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.

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.

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.

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.

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.

The truth has many meanings

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!

10 Rhodium plating – the most frequently asked questions


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I was told that the reason my rhodiumwore off my bracelet so quickly is dueto the perfume I wear. Is there any truth to this?

I want to have a yellow gold chainbracelet re-plated, how thick should the rhodium be and how long can I expect it to last?

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

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?

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.

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.

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.

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

Rhodium plating – the most frequently asked questions, part 2


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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.

Its really about the fundamentals

The rhodium coating shall have adequate density and free of voids.Spec # 4

Density of the rhodium coating ultimately determines the level of protection andactual 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 regionsand hard to reach areas on an item of jewelry (I.e. inside surface of wedding band).

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.

Spec # 2 The rhodium coating shall be only applied to clean and active surfaces.

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

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!

Sometimes hot tubs are not cool!

The rhodium coating shall be of adequate thickness.Spec # 3

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

12 Plating specifications for decorative rhodium coatings


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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 a rhodium coating 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!

In the final analysis, it’s the results!Often one of the first plated areas of a ring that fails arethe tight junction points. Low current density sometimes does not allow adequate deposition of the rhodium layer.

A key area where perfume, hand cream, and dried soapsaccumulate. Their chemistry can slowly attack the nickel in the white gold alloy.

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!

Another recessed area that typically does not receive adequate thickness of plated rhodium.

This location on the inside of the band is often one of the firstareas to wear off. High incidental contact at back edges of the ring quickens the wear off process.

This is a high contact area and often will wear off first.Tiny scratches will start tomake the diamond look dull.

Frequently the starting point forcorrosion attack by chloride ionssecreted from skin perspiration. Corrosion process is accelerated by too much time in the chlorine environments (I.e.hot tubs).

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 viableprotection is possible. A tiny breach anywhere in the rhodium will allow chloride ions from the skin to start the reaction process to the nickel.

Fig1.

Fig 2. Fig 3.

13 Key considerations for the rhodium plating of jewelry

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