This is the second part of my Blog on the removal of tarnish from silver jewellery. Please click here to read the first part (Number 10)

In the previous part (1) I gave a brief overview of the element silver, what tarnish is and how it occurs and I looked at two methods of removing tarnish: by using an impregnated polishing cloth and by using a chemical solution, or silver dip.

In this second part I will be looking at two further methods. The first one is an interesting process that can be done easily at home with baking soda/washing soda, hot water and aluminium foil and various recipes can be found online.

Electrochemical process (Sodium Bi/Carbonate and Aluminium Foil)

In this process, a ceramic bowl is lined with aluminium foil and a solution of baking soda (sodium bicarbonate) or washing soda (sodium carbonate) and hot water, into which the tarnished piece is submerged. I did experiments with both sodium bicarbonate and sodium carbonate and did experiments to find out for well both works.

“The process is electrochemical, with the carbonate solution acting as the electrolyte. As long as contact is maintained between the two metals, the aluminium corrodes and hydrogen gas is produced. This gas then reacts with the tarnish, reducing it back to the silver metal.”[1]

The object of my experiments was to find how I could remove tarnish from textured surfaces, pieces with a satin finish and those with Keum-Boo patterns.

I tarnished a few silver test pieces with the boiled egg method[2]. All silver pieces had a deep, dark-brown tarnished surface. These pieces were also textured, some lightly, some more heavily and some also had 24ct gold Keum-Boo gold patterns.

I lined a ceramic bowl with aluminium foil, added circa 300ml hot water and then a table spoon of sodium bicarbonate / sodium carbonate. I placed the tarnished pieces into the solution and left it for 10 minutes. After this period I lifted the piece out and rinsed it with ionised water.

One can see a brownish rim on the aluminium foil in the bowl which is the removed tarnish.

Baking Soda (Sodium Bicarbonate)

This solution worked well for lightly tarnished surfaces, but it struggled with tarnished pieces that had a deeper brown colour. Even after repeating the process with fresh solution was the tarnish not completely removed.

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Washing Soda (Sodium Carbonate)

In the experiment using sodium carbonate I used three pieces I had used in previous tarnish removal experiments as well as one ‘new’ one. All pieces were tarnished with the boiled egg method (see footnote 2) and had a deep brownish-black colour. They were left in the sodium carbonate solution for 10 minutes. After this period most of the tarnish was removed from the ‘new’ piece, whilst the other three still showed quite a bit tarnish.

In summary, this process works well for lightly tarnished pieces, or as a first step of removing some tarnish, to then be followed up by a second method.

Washing soda (sodium carbonate) is a substance that occurs naturally and its safety data sheet classes it as not dangerous for the environment, indeed it is often used as an eco-friendly cleaning agent in the home. Despite this, care must be taken when using it as it can be an irritant for hands and eyes.

Baking soda (sodium bicarbonate) works similarly to washing soda and it is also considered a very safe, biodegradable and eco-friendly cleaning agent.

Other Methods: Precipitated Calcium Carbonate

When researching this subject I came across various documents online published by the Canadian Conservation Institute (CCI). These dealt with different processes of removing tarnish from museum objects and were very thoroughly researched papers and very valuable for this blog.

These papers explained in detail the various aspect on how tarnish occurs, how it can be prevented and how it can be removed.[3]

In relation to removing tarnish it also mentioned another method which falls into the first category of using mechanical action. The substance used here is precipitated calcium carbonate – super-fine chalk (CaCO3).

The article explained, amongst other things, that silver sulphide (tarnish) is a somewhat softer than the actual silver and that calcium carbonate is slightly harder than silver. This make it an ideal and still very gently abrasive to use to remove tarnish.

What is Precipitated Calcium Carbonate (PCC)?

Calcium carbonate (chalk) is a naturally occurring substance. “It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor.”[4]

“Precipitated calcium carbonate (PCC) is an innovative product derived from lime, which has many industrial applications.  PCC is made by hydrating high-calcium quicklime and then reacting the resulting slurry, or ‘milk-of-lime’, with carbon dioxide.  The resulting product is extremely white and typically has a uniform narrow particle size distribution.  PCC is available in numerous crystal morphologies and sizes, which can be tailored to optimize performance in a specific application.”[5]

Is PCC eco-friendly?

The Safety Data Sheet by Thermo Fisher Scientific, one of the companies selling this product, states that PCC does not pose any health or environmental hazards.

As the chalk is a very fine powder care should be taken not to inhale the dust, but as it is mixed with water this risk is somewhat reduced. Rubber gloves should be worn when using it as the powder is abrasive on the skin.

How is it used?

PCC is mixed with tap water to make a paste and is then rubbed over the tarnished surface with a soft cloth.

The substance will turn greyish and it should then be rinsed off with clean tap water. Afterwards the piece should be thoroughly dried.

Results:

I made a paste as described above and used it on some of the above-mentioned tarnished pieces on which the sodium bicarbonate/carbonate and aluminium solution did not fully remove the tarnish.

The calcium carbonate worked very well on all the test pieces. It removed the tarnish completely. The pieces became slightly shinier after the treatment but the surface felt whiter - in comparison to using a polishing cloth.

None of the methods used above were able to retain a previous matte surface finish on the piece.

I contacted the CCI to find out about any specific methods of removing tarnish from matte surfaces. They replied saying that they had no methods of removing tarnish and preserving the matte original surface finish of a piece.

Conclusion:

Removing tarnish from silver can be done in various ways. In terms of their environmental impact or hazardous nature, the most hazardous is the silver dip.

Using a polishing cloth, sodium bi/carbonate and calcium carbonate are low impact methods of removing tarnish, however they may differ in their effectiveness.

Lightly tarnished objects can be cleaned by using polishing cloths or the sodium bi/carbonate, aluminium foil method. For more stubborn tarnish precipitated chalk is a good way of removing tarnish.

I have not found a method of removing tarnish from matte surfaces whilst preserving the matte finish. The matte surface finish would have to be re-applied after tarnish removal. For the customer, those pieces of jewellery should best be given to a jeweller who can restore the previously matte surface finish.

I hope you have found these two blogs interesting. Do let me know if you have any comments.

[1] (Silver – Care and Tarnish Removal – Canadian Conservation Institute (CCI), Notes 9/7, (2019) https://www.canada.ca/en/conservation-institute/services/conservation-preservation-publications/canadian-conservation-institute-notes.html )

[2] As hard-boiled eggs contain and release hydrogen sulphide, they can be used to tarnish objects quickly. Though it is less predictable, it is an eco-friendly way to darken pieces of jewellery. All pieces developed a speckled brown hue which may have been due to the condensation of water inside the closed box.

[3] See footnote 1 above.

[4] Wikipedia: https://en.wikipedia.org/wiki/Chalk

[5] https://www.lime.org/lime-basics/uses-of-lime/other-uses-of-lime/precipitated-calcium-carbonate/

In my 10th (October) Blog I wanted to write about the removal of tarnish from silver jewellery. However, October and November have been busy months and I did not manage to finish this piece.

Now, at the end of November it is almost finished but it has once more become a lengthier article and so I decided to divide it into two, more manageable pieces.

Motivation

As to my motivations for writing about this topic: When I set up my website I wrote a section for my customers (or those interested) on how to look after their jewellery. I covered tarnish removal but recently felt that it could do with updating.

More specifically, I wanted to investigate methods other than using a polishing cloth and those which worked well on textured or satin surfaces. I did some research and conducted some experiments to see which methods worked, were environmentally friendly and could be replicated at home.

What is tarnish?

Silver is a white metal which has been widely used throughout the ages. Its sought-after qualities include its high lustre, reflectivity, superior thermal and electrical conductivity as well as very good malleability and ductility.

Silver is an element with the symbol Ag, lies within Group 11 and Period 5 of the Periodic Table and has the Atomic Number 47. In its pure state silver is very soft, making it often impractical for use in jewellery. It is therefore alloyed (mixed) with copper which makes it harder and produces what we term Sterling Silver. The ratio of metals in Sterling Silver is 925 parts pure silver and 75 parts copper.

Pure silver barely reacts with oxygen, however, it reacts with sulphur-containing gasses in the air. The most common is hydrogen sulphide (for example contained in hard-boiled eggs, decomposing plants or animals.) Silver reacts with this gas and produces the compound silver sulphide (Ag2S) and it is this, we define as the brownish-black tarnish on silver. (In Sterling silver the reaction with hydrogen sulphide also produces copper sulphide (Cu2S).)

Tarnish, therefore, is the result of a chemical reaction between a metal and a gas

Early silver Athenian coin, 5th century BCE. British Museum. By I, PHGCOM, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2392720

Which metals are affected and why?

Tarnish can affect different metals. Copper, brass and aluminium can also tarnish through their exposure to oxygen or other gases, but silver needs hydrogen sulphide to form this dark layer of tarnish.

Unlike rust, however, the tarnish layer actually protects the inner layers of the metal from further tarnishing. A newly polished piece of silver, therefore, tarnishes quicker than an already tarnished piece. However, tarnish changes the original appearance of the piece and this is why most people would like it removed.

Traditional methods of removal?

There are many ways in which tarnish can be removed from silver once it has occurred, though it is best to prevent the tarnish from occurring in the first place. This can be achieved by storing the silver article in a sealed plastic bag or container, thus avoiding contact with air which may contain hydrogen sulphide.

To remove tarnish, once it has occurred, the following methods have traditionally been used to remove tarnish from silver:

• by mechanical action of polishing the silver, using a silver polishing cloth

• by immersing the silver into a chemical solution (silver dip)

• by an electrochemical process, involving baking soda, water and aluminium

Before any tarnish is removed, the piece should be gently cleaned with warm soapy water and a soft cloth or toothbrush to remove any other dirt particles that may have accumulated.

Mechanical action – Polishing Cloths

All mechanical polishing action involves some kind of abrasive particles to remove the tarnish (as well as some silver), although some products are gentler than others. It is advisable to check on a test piece how aggressive or not your chosen product is.

Polishing cloths are soft cloths that are impregnated with a polishing compound which removes the tarnish and usually also a tarnish inhibitor which prevents (or slows down) tarnish from occurring.

These cloths are very gentle and are a good way of removing light tarnish from your silver jewellery and they work particularly well on polished surfaces. They can also be used on textured surfaces but on coarser textures or heavy tarnish they may not be able to remove all the tarnish. Using them on matte or satin surfaces will result in the surfaces being shinier than before.

Polishing cloths can also be used on pieces with 24ct gold Keum-Boo patterns. The surface will become shinier than the original finish.

Chemical solutions (silver dip)

These chemical dips are available from different companies. They work by immersing the tarnished piece of silver into the solution for a couple of minutes and then rinsing and drying it. The tarnish will have been removed.

They are not suitable for all items, especially if other materials or gemstones are included in the piece.

These dips contain an acid (in the brands I compared, these were hydrochloric acid and sulfuric acid) and other chemicals that may be harmful to the user. In the safety data sheets of two different brands I compared these substances were classed as hazardous to health.

Due to these chemicals these solutions are very difficult to safely dispose of after use.

- To be continued in Part Two -

In July I had planned to write a blog on Keum-Boo, however, when I got around to writing it in August it became quite long.

I therefore divided it into three different ones: The first was about Hallmarking (Blog 7), the second (Blog 8) about the Keum-Boo process and this, the third, is on the subject of gold plating.

Both issues of hallmarking and gold plating are relevant to discussing Keum-Boo and I wanted to explain my thoughts on this.

Gold Plating Process

An oval brooch and ear studs from my current collection using the Keum-Boo technique.

Plating is an electrochemical process in which a thin layer of a chosen metal is deposited onto a base metal. Most often plating is done in gold, but is also done in rhodium or non-precious metals which may be applied as an undercoat before the gold is applied. In this blog I will mainly concentrate on gold plating.

The thickness of this plated metal layer can vary and is measured in micrometres, or short microns.

1 micron (1 μm) = 0.001 mm (As a comparison, a human hair is circa 75 μm thick.)

Before any gold plating can be done, the piece has to be thoroughly cleaned in various stages and this involves solvents and abrasive processes, after which the piece is dipped in hydrochloric acid. The now thoroughly clean piece is then lowered into a bath containing metal salts. This is the actual plating process:

“An electric current is placed through this bath and is directed at the object. The current helps to dissolve the metal molecules and deposit them onto the object in the bath. The longer items are left in the bath with the current, the thicker the plating level will be.”[1]

The metal salts used in this solution are created by combining metals and acids. The neutralising reaction of an acid and a base results in metal salts. As acids Aqua regia (a mixture of hydrochloric acid and nitric acid) or Potassium gold cyanide can be used (see image on the left). When gold is dissolved in Aqua regia toxic fumes are created as a by-product. Potassium gold cyanide is highly toxic and its handling can result in poisoning through contact with eyes or skin and through inhalation or ingestion.

Disposal of these toxic acids is difficult and problematic for the environment.

In one of my past collections I used a specialist to have my pieces gold and rhodium plated. However, becoming aware of the environmental impact of gold plating I wanted to avoid this process altogether and so I looked for alternatives.

After some research I came across the Korean Keum-Boo technique and liked its straight forward process, the potential it offered for creating patterns but also, most importantly, that it appeared to be a clean process.[2]

In simple terms, the Keum-Boo process describes the bonding of 24ct gold foil (which is 13 microns thick) through heat and pressure to silver.[3]

Gold Plating Names and Thicknesses

In my previous Blog 7 on Hallmarking I noted that in the UK silver articles containing gold can only be hallmarked as containing gold when the gold layer is above 100 microns.[4]

Consequently, the Hallmarking Act does not distinguish between the different thicknesses of the gold plated layer. Whether the gold layer is 0.175 microns or, as in Keum-Boo, 13 microns – both are regarded as plating.

This has a bearing on my pieces in which I use Keum-Boo. As the gold layer is 13 microns thick – well below the required 100 microns - they can only be hallmarked as silver.

As the price of gold has risen over the years, jewellery made from solid gold is unaffordable for many. Adding a thin layer of gold over a base metal to give the appearance of gold but without the high price is therefore a very attractive option for many customers.

It can, however, be very confusing to distinguish between the different labels used by jewellers to describe their gold-plated pieces. They may come across words such as, Vermeil, Rolled Gold, Gold-filled, heavy gold plating, flash plating and of course Keum-Boo. Below, therefore, a brief explanation of the different terms:

Beforehand, however, a few notes to explain various differences.

Base material

As described above, in the gold plating process, the gold layer is added over a base metal. In cheap pieces the base metal is often copper, brass, zinc, etc., whilst in more expensive items it tends to be silver. Plating is also often applied to a gold base – a good example here are white gold rings which are plated with rhodium to give them the white lustre so desired.

Plating thickness

Different pieces of jewellery are plated in different thicknesses, dependent on their use. Pieces that are subject to greater wear and tear, for example rings, are plated more heavily, whilst earrings have a thinner coating. Earrings are typically plated with 0.175 - 1 microns, necklaces usually with 2 microns and rings with 3 - 5 microns.

When buying jewellery, it is worth bearing in mind that plating rubs off eventually and this is especially so for pieces that have to withstand a lot of wear and tear, for example rings and especially wedding rings. When the plating rubs off, the base metal is revealed and the piece has to be re-plated to restore its original beauty.

Legal requirements of gold plating

Countries have different legal requirements when it comes to hallmarking and the description of gold plated articles. This can be quite a confusing aspect when shopping online for jewellery as it may not be immediately clear where the company is based (and what the legal requirements there are), or whether the customers of a particular company are mainly based in another country.

I have, for example, come across online companies based in the UK, which also trade abroad. Their description of certain gold-filled articles states the adherence to certain legal requirements which - although they may apply in countries, such as the US - clearly do not exist in the UK.

Whilst in countries, such as the US and Canada, the use of certain words describing plating is defined by law, there are no such requirements in the UK. In a conversation with a specialist from the Birmingham Assay Office, the gentleman explained that there is no legal minimum or maximum thickness when it comes to plating.

There are, however, regulations as to how a piece can be hallmarked and described and this must be done so as to avoid any confusion for the customer. In the UK, all gold layers under 100 microns are regarded as plating and therefore cannot be hallmarked as gold.[5]

Vermeil

The word Vermeil is used to describe gold-plated articles. Whilst in the UK there are no such legal requirements, in the US this word can only be used to describe pieces of jewellery that are made of silver and which have been plated with a thickness of at least 2.5 microns and with at least 10ct gold.[6]

Gold-Filled or Rolled Gold

The term gold-filled or rolled gold is a little confusing. The metal is not literally ‘filled’ with gold but a layer of gold is mechanically bonded to the base metal. This base metal is usually brass and the gold layer can be of any gold alloy, but is often 14ct gold.

Again, US laws define the legal gold content of such articles which are to be sold in the US. The thickness of the gold layer is not given in microns but is expressed as a ratio of the overall weight of the piece. The gold content of a gold-filled item has to be 1/20 of the whole weight or, in other words, 5% of the total weight of the metal item.

This is quite a confusing method of describing the thickness of the gold layer and attempts to calculate the actual thickness concluded that the gold contents of the layer would roughly equate to the layer of gold in the Keum-Boo technique.[7] The fact remains that the base layer is brass, which is an alloy of copper (66%) and zinc (34%), chosen presumably because of the similar colour to gold which would hide any partial wear of the gold layer.

Due to the complex manufacturing process of gold-filled metals, articles made from this material are usually mass-produced.

Gold-filled jewellery can be hallmarked in the US – not the UK – and the hallmark would read, for example: 14K 1/20 GF. This would translate as follows: the piece is coated with a layer of 14ct gold to a thickness of 1/20 of its total weight, i.e. is Gold-Filled.

Heavy gold plating

This term refers to the thickness of the gold plated layer, specifically a thickness above circa 2.5 microns.

Flash plating

Flash plating is an extremely thin layer of gold that would wear off very quickly and refers to a thickness of less than 0.125 microns.

Silver gilt

Silver gilt or gilded silver refers to the coating of silver with a fine layer of gold. It is often interchangeably used with the word ‘vermeil’, mentioned above. The word ‘gilding’ is also used to describe the covering of various other materials (wood, ceramic, metal) with gold leaf. Gold leaf refers to ~23ct gold with a thickness of circa 0.125 microns.

Fast Jewellery

Photo of costume jewellery by Martin de Arriba on Unsplash

Considering the above, it is important to note that gold plating also has a significant environmental impact – in addition to the toxic chemicals used in the process - through its role in the creation of fast jewellery. Fast jewellery describes cheap jewellery sold by High Street chains, which imitate more expensive items, for example, by being gold-plated.

Ruth MacGilp who wrote this article for Eco Warrior Princess, an online media brand, sums up the problematic nature of fast jewellery:

“Despite this progress towards more conscious collections, ultimately fast jewellery by its very definition is about quantity over quality. With ‘drops’ of shiny new pieces every week and prices lower than a cup of coffee, we’re lured into the familiar trap of hyperconsumption. Our broken tortoiseshell earrings and tangled pendants simply pile up in landfill, soon to be replaced with something more worthy of the Instagram like button.”[8]

To illustrate the above, I did a quick online search of the jewellery section of a well-known High Street fashion brand and found a pack of nine gold-coloured rings for £6.99. Information about the materials used was not very detailed. It stated they were: Metal 55%, Steel 45%. This does not make any sense to me, nor is it particularly helpful.

One can expect the thin gold layer of these rings to rub off in a matter of weeks, after which the rings will probably be never worn again. Unethical, non-transparent working conditions or processes during the manufacture of these pieces further add to the problem.

Keum-Boo vs Gold plating

In summary, it is clear from the above that there are serious concerns with gold plating. From the use of toxic chemicals, such as Potassium gold cyanide, to its environmental impact through the creation of Fast Jewellery, gold plating plays a huge role in how the jewellery industry affects the environment.

How does the Keum-Boo technique that I use in my pieces compare to gold plating? I believe the advantages of this technique over the plating process are as follows:

1. The Keum-Boo process[9] has very little impact on the environment. The chemicals I use in this technique are baking soda, methylated spirit, pumice powder and citric acid (which I use as my jeweller’s pickle).

2. The required heat comes from an electric hot-plate and the necessary pressure from the agate burnisher and my hand.

3. The 24ct gold foil I use in this process originates from a Japanese company which recycles gold from the dental and electronics industries.

4. The gold foil is 13 microns thick – up to 10 times thicker than standard gold plating. This thickness ensures that the gold layer will not rub off easily and will last a long time.

5. When designing the piece and the patterns thereon, I pay special attention to the wear and tear of the item. For example, I would not add the gold foil on such parts that are subject to a lot of wear and tear, such as ring shanks where the gold would rub over time.

6. Whilst the process of this technique can be compared to gold-filled or rolled gold, my pieces are made from either recycled Sterling Silver or recycled Fine Silver and not brass as in gold-filled articles.

7. Whilst I would be able to cover an entire piece in gold foil with the Keum-Boo technique, the main reason for using this technique is that it gives me the artistic freedom to create patterns on my pieces using the beautiful colours of both metals, which are otherwise difficult to create. Gold plating could not achieve this.

8. The jewellery I create is made by myself in my own studio and I try to be as transparent and eco-friendly as I can in my working practices.

9. I make small collections or one-off pieces and each piece is made so that its design and materials can speak for themselves and will stand the test of time.

Thank you for reading! I hope this information was useful. If you have any comments or question, do let me know.

Examples of pieces from my current collection Interrupted Patterns in which I use the Keum-Boo technique. Click on the images for further information.

[1] https://sciencing.com/causes-gold-discoloration-6158003.html

[2] Read my Blog 6 ‘Interrupted Patterns’ on the significance of patterns in my most recent collection.

[3] For a more detailed description see Blog 8 on Keum-Boo.

[4] In such cases, along with the silver hallmark, a part-mark will be applied to the piece, stating the hallmark of the second metal.

[5] See here my Blog 7 on Hallmarking, contact any of the Assay Offices or see the Guidance Notes on Hallmarking.

[6] The US Code of Federal Regulations 16, Part 23.4 on the Misuse of the Word ‘Vermeil’ states “(b) An industry product may be described or marked as “vermeil” if it consists of a base of sterling silver coated or plated on all significant surfaces with gold, or gold alloy of not less than 10 karat fineness, that is of reasonable durability 33 and a minimum thickness throughout equivalent to two and one half (2 1/2) microns (or approximately 100/1,000,000ths of an inch) of fine gold.”

[7] The calculations are further complicated by the different special gravity of the base materials (to calculate weight) and the use of different gold alloys in the comparison. Keum-Boo uses 24ct gold, 13μm thick over a silver base; whilst gold-filled articles use, for example, 14ct gold over a brass base.

[8] https://ecowarriorprincess.net/2020/06/fast-jewellery-true-cost-of-costume-ethical-pieces/ (Ruth MacGilp, 16 June 2020)

[9] For details on the process see Blog 8.

My second blog for August is on the Korean technique of Keum-Boo – the main subject I had intended to write about in July. As it was a busy month I didn’t quite manage to post it. Whilst writing it, I also realised that it had become too long, so I divided it into three: one on Hallmarking, the second one on Keum-Boo and the third (in September) on gold plating.

Origin

Keum-Boo is an ancient metal work technique which originated in Korea, though the exact beginnings are unclear. Keum-Boo (also spelt Kum-boo or Kum-Bu) literally means ‘attached gold’. This technique is about attaching pure, 24ct gold foil to silver.

So, why am I using this technique? I came across it when trying to find alternatives to gold plating. (Look out for my next blog in September!) In one of my past collections I had various pieces gold/rhodium plated but when I came aware of the environmental impact of gold-plating, I wanted to avoid using this technique and looked for other ways of adding gold patterns to my work.

I came across Keum-Boo online, when researching alternatives and was immediately intrigued and struck by the potential it offered for creating gold patterns (see my Blog 6 where I wrote about my fascination with patterns) and also the way it did not involve hazardous chemicals.

Keum-Boo

What attracted me further to this technique was its simplicity. I like learning new processes, but especially so when they do not involve the necessary purchase of expensive tools and equipment.

The things I needed for Keum-boo was pure, 24ct gold foil, one of my pieces of sterling silver jewellery, a hot plate, fine scissors, tweezers, baking soda and methylated spirit. The only new tools I needed to buy were two agate burnishers - beautiful objects in themselves (see below).

The gold foil I use for Keum-Boo is 13 microns thick = 0.013 mm. (The thickness is measured in micrometers, or short microns: 1 micron = 0.001 mm.)

Compared to the thicknesses of 0.5-5 microns for gold plating, this gold foil is quite substantial. In actual fact, when I cut my gold foil pieces I always feel I can sense the weight of the gold when it falls onto the table.

The gold foil I buy is recycled and comes from a Japanese company that recycles gold from the dental industry and from electronic scraps.

I have recently also invested in a digital micrometer so that I am able to recycle and roll down my own gold to the correct thickness.

Keum-Boo Process

Keum-Boo is usually the last thing I do on a piece – in other words, all other fabrication steps have been done before. The silver is then prepared to receive the gold. When using sterling silver (as it is an alloy containing copper) it has to be prepared so that a thin layer of fine, pure silver at the surface is created. This allows the fine gold molecules to bond with the silver. When using fine silver, this step is not necessary as the fine silver is pure and does not contain copper.

Once this has been done, the piece is cleaned with baking soda and methylated spirit. I then cut the relevant shape from the gold foil which requires patience and calmness. (Pet cats that jump onto the worktop with the gold foil laid out should be avoided here, as are open windows and sudden gusts of wind. ;)

During the design stage, I would have finalised the exact pattern I want to create and this will guide me when I am cutting the foil.

When all is prepared, the silver piece is placed on the hot plate and the gold is laid on top. Whilst holding the silver piece in place (and this is often the really tricky bit), the gold is burnished (pressed) onto and into the silver with the agate burnisher.

When I am sure all areas of the gold are properly attached, I remove the piece from the hot plate, allow it to cool and add the finishing touches.

Please note that working over a hot plate involves getting very hot! Therefore, it is most beneficial to do this when one is cold - crouching over a hot plate in the summer and doing a collection of 20 pieces in 30°C is challenging! It is paramount to wear gloves to protect the hands from the heat and ideally a face heat guard to protect the eyes from exposure to heat from the hot plate. The images below show the making process of a pair of square stripy ear studs which are available to buy from my shop.

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Below are various pieces from different collections that I have made using this technique.

Book classes

If you are interested in learning this technique do get in touch by email and I will let you know when the next course is planned. I usually teach this technique over a whole weekend at Rachel Jeffrey Jewellery in the beautiful village of Wheathampstead, Hertfordshire. During the course I will explain the technique in great detail and there will be plenty of time to make a number of pieces. I will also teach the additional technique of riveting that can be used in combination with Keum-boo.

July was a busy month for family matters, so I didn’t manage to post a blog. I started writing the August blog but as it became longer and longer I decided to split it into three more manageable blogs: two for August and one for September.

I will start with a short blog on Hallmarking. Hallmarking is a complex matter and can sometimes be mind-boggling.

The hallmarking process in the UK is regulated by the Hallmarking Act 1973. Whilst there are some exceptions, the Act states that I must have my pieces hallmarked if I want to sell them and describe them as being made of precious metals.

The Assay Office tests the pieces to ascertain that they are indeed made of the metals the maker says they are. When satisfied this is the case, the Assay Office applies the hallmarks to the piece.

There are a various options on how many marks are applied but at the minimum they must contain the following three marks: the maker’s mark, the metal/fineness mark and the mark of the relevant Assay Office.

Below you can see three marks: the first mark (maker’s mark) is composed of the letters of the maker. You can see my own mark here, which contains the letters HBM within a rounded rectangle. Each of the maker’s marks are completely unique and refer only to one particular maker. The second mark concerns the metal fineness - in this case, it is sterling silver (925). The third mark is the symbol for the relevant Assay Office - here, the London Assay Office with whom I am registered.

The Hallmarking Act also states that precious metals can only be hallmarked as the relevant metal if it is thicker than 100 microns[1]. This has an implication for some of my pieces in which I use the Korean technique of Keum-Boo - please see the images below. (My September blog will focus on this technique.) In this technique a 24ct gold foil with a thickness of 13 microns is heat-bonded to the silver.

As this foil is less than 100 microns thick, my Keum-Boo pieces can only be hallmarked as silver.

For a complete guide to hallmarking, please see the Dealer’s Notice (below) the Guidance Notes on the Hallmarking Act or see the website of the London Assay Office who hold my hallmark.

This blog will also appear as a new page on my website.

[1] The thickness of gold plating or any other metal layer is measured in micrometres, or short microns. 1 micron = 0.001 mm