This video and article are an introduction to the material of vitreous enamel itself, which metals can be enamelled, what reactions we can expect when enamelling these metals, a quick primer on firing methods, and a brief review of the different techniques, with a tiny bit of history. I think these are the bare basics you need to know if you want to get started with enamelling.
I actually scripted and recorded this video three times. The last edit was intensely streamlined and simplified. Video works wonderfully to show and teach processes and techniques, but it is really not the best medium for theory and lists of facts, its is just not easy to follow the content. So the final version of this introduction video is much more minimalist, and I decided to expand on it in article form, which is what you are reading now. I do recommend that you watch the video first, it is not very long. You will find more expanded information and pictures below, which you can go through and process at your own pace.
Before we continue, let me add that I am not a chemist and this is intended as a guideline only.
Vitreous enamel, as the name implies, is a type of glass, and it is formulated to adhere to the surface of metals. We use it as a ground powder, which resembles sand, and after application with dry or wet techniques, it is fired at a high temperature in order to vitrify it, to fuse it into a glass layer over the metal base. This is done for artistic, decoration or functional purposes.
Glass is made out of silica, which is found in nature as quartz. But silica melts at no less than 1700 degree centigrade. Copper melts at 1080, gold at 1060 and silver at only 960!
Silica > 1700°C > 1958°F
Copper > 1080°C > 1976°F
Gold > 1060°C > 1940°F
Silver > 960°C > 1760°F
So, silica melts at a much higher temperature than our metals, and of course this is a problem. Something needs to be added to silica to lower the melting point. The materials added to do this are called fluxes, and an example of one of these fluxes is boric acid. Maybe you have heard the term borosilicate glass, this name indicates there are two main elements that constitute this glass, boron and silica. Other materials are added to the formula to make the glass more stable, insoluble, modulate the viscosity and very importantly, the coefficient of expansion (this means the rate at which stuff expands and contracts when it is heated or cooled down). Different materials are used to change all these properties, and enamels for different metals have different properties.
Other additives also change the properties of opacity and colour, and these are very important for artists. For colouring effects, metal oxides are added, like for example cobalt oxide for blue and gold salts for red.
To manufacture enamel, these elements are melted together in a furnace to produce what is called frit. The purpose of this pre-fusion is to render any soluble and/or toxic components insoluble by causing them to combine with silica and other added oxides. Thus, the most dangerous part of the enamel process is done in factories under strict safety and environmental conditions, and the product we buy is relatively safe to use.
During this process many of the properties of the enamel are influenced by not only the materials used, but also the type of furnace they are melted in (for example, there may be more or less oxygen present) and the temperature reached. This then determines how the enamel will behave and look when we work with it later.
Once melted the frit is scooped up and poured into “cookies” on metal tables, and then crushed into chunks and further processed into smaller chunks, which are best for long term storage, or ground to a mesh (standard mesh is 80) that is ready to be used by the enameler, and which looks like sand.
From here on, we purchase these chunks or powder and we can grind it, sift it or wash it and use on our prepared metal surface.
The main types of enamel you can use are transparent, opalescent and opaque.
Flux is a particular type of transparent enamel which is especially formulated to a specific metal, to be applied directly on top of the metal. It may absorb the firescale if necessary (for example copper flux does), and acts as an isolation layer to avoid discolouration effects, which we will go into later.
A transparent enamel will let the light pass all the way through to the metal below, and it will typically have a colour to it, from very pale to so intense it may almost look opaque.
Opalescent enamels are halfway between transparent and opaque, they have a milky, misty appearance that makes us think of the precious stone opal, which is where they get their name from. These are tricky to fire, typically increasing in opalescence with more heat or time in the kiln. You can learn more about these enamels in my video class about the opalescent grisaille technique, and I will get back to it again in the future to cover other aspects.
Opaque enamels do not let light through. They’re quite forgiving, and since the base metal is not visible, they’re often used on copper and steel, although very interesting design effects can of course be achieved by using them in combination with all the other types of enamel.
Finally another aspect that I must talk about is leaded and unleaded enamels. Lead used to always be a component of enamel until more recent decades, in which concerns for toxicity and environmental impact saw the development of unleaded versions.
It is a question often asked, if leaded enamels are superior to unleaded enamels.
Reportedly leaded enamels are more brilliant and a wider color palette can be achieved, and for example opalescent enamels are leaded. But some other interesting effects can also be achieved with unleaded enamels and some workshops work exclusively with them due to safety reasons.
Indeed breathing in powdered enamels, no matter the type, is hazardous, since silica is insoluble and remains in the lungs, and other hazardous elements are present. When sifting, that is, dry application of enamel, to wear a mask especially fit to this purpose (fine particulate) is always recommended, and airborne powder in the workshop can also be limited by good hygiene practices and working with wet applications. In my personal work I use leaded enamels and I rarely sift, my preferred application mode being wet-packing.
Once fired, all these materials are considered to be encased into the glass matrix and safe to be around. However enamel is not considered food safe and should be used only for decorative and artistic items. A notable exception to this is industrial enamel especially manufactured and tested to be food safe and used for cooking, serving and household items.
It is always your personal responsibility to research the safety of the materials you use in your work, and make informed decisions about which materials to choose and how to work with them.
So, which metals can be enamelled? Many, for example there are enamels formulated for aluminium. But the metals that are commonly used in artistic and jewellery enamel, which is the focus here, are the classic ones: copper, silver and gold. Iron and steel have in the past been used mainly in industry, like you’ve seen in old school bathtubs and kitchen implements, but in recent decades there’s been renewed interest in using these metals also for artistic purposes due to their special qualities and/or their lower cost.
To enamel on iron or steel, you need a special ground base coat. This goes on opaquely over clean metal. Once the ground is fired, you can use industrial, liquid or other types of enamels on top, but you can also use the vitreous enamels formulated for non-ferrous metals. So you can take a commercial enamelled mug and enamel on it! In fact a lot of people that work with steel just use pre-enamelled panels, which are available in white or other opaque colours. These are great for very large format work.
Let’s move on to copper, silver and gold.
Preferably you will choose electrolitic 99% pure copper to enamel on, since contamination with certain other metals can give you a lot of trouble, say if you recycle copper from construction materials. It can be done but it is risky.
When it comes to silver, fine silver, that is, 999 out of 1000 parts silver, is also the finest choice, but this metal is very soft on its own and that can sometimes be a problem, so most jewellery you’ll find is sterling silver, an alloy, especially rings and bracelets which need to be sturdy.
Gold is the best metal to enamel on! Pure gold is 24k, 24 karats, which is how gold proportions are measured, so 24 parts out of 24. Pure gold is a very soft metal and often alloys are used, like 22k, 18k etc. Also gold is super expensive! Currently about 100 times more expensive than silver.
Copper tarnishes in contact with the atmosphere, you sometimes get a patina in reaction with chemicals in the air, like you’ve seen in green copper roofs – and this can also be done on purpose of course, you can apply chemicals to copper or bronze and this way achieve a huge variety of colour.
When heated up, in the presence of oxygen in the air, a black oxide forms on the surface of copper, this is called firescale. This oxide can be a problem when enamelling, although it can also be the source of cool effects, so most often it is carefully removed before enamelling. When firing the first layer of enamel again firescale is produced, and you will see the surface becoming black, and then the oxide being dissolved into the enamel flux, which is formulated for this purpose. On the next layers, the surface of the metal, where covered by enamel fused to the surface, is not in contact with oxygen from the air anymore, so no further oxide is formed.
Pure silver slowly tarnishes in contact with sulphur in the air, but not when heated up.
Pure gold doesn’t ever tarnish!
So what is an alloy? A mixture of metals molten together. This is done for many different reasons. One is to reduce cost, but that’s only part of the equation. When you mix two or more metals, their properties change, sometimes in surprising ways. Silver and gold alloys are much harder and thus durable than they are when pure.
A couple of very common alloys are sterling silver and 18k gold.
Sterling silver is 925 parts silver out of 1000, and the rest, most often, is copper.
18k gold can have many different proportions of metals, as long as 18 out of 24 parts are gold (so 75% gold). A common 18k yellow gold alloy is 75% fine gold, 15% copper and 10% fine silver.
Both of these alloys can be enamelled, but since both contain proportions of copper, they both get firescale when heated up.
A so called “green” gold alloy is 18 parts gold and 6 parts silver, and there being no copper, there is no firescale, which is ideal.
The firescale in these copper-bearing alloys is not as strong as on pure copper since the amount of copper is small, and often the enamel will absorb it with no problems, although the colours might not be as brilliant as on pure silver and gold, but for jewellery purposes sometimes concessions have to be made in the name of strength and durability. This will depend on the design.
One way to get around these tarnish problems is to perform an operation called depletion gilding, in which copper is removed from the very surface of the metal.
Another thing to have in mind is that these alloys are often the product of casting processes. In these we might have problems of porosity, depending on the technology used, and this can be a huge source of headaches. Burnishing the surface might help, as is done also when enamelling precious metal clay, which is fine silver but also very porous.
Also of note, fine silver and fine gold are often used in the form of foil and wire for specific techniques. In these cases the softness of the material is not relevant, since they’re placed between layers of enamel, and thus it is very nice to use the pure metals.
Brass! Yes you can enamel brass. Brass is an alloy of copper and zinc. Zinc is an enemy of enamel. However, when the concentration of zinc in the brass is small, we can enamel it. Traditionally, medals, both military and civilian, and badges of many kinds, for example for cars (and this is still done for luxury cars) were enamelled on what is called gilding metal, and then gold or silver plated. This is a brass with a low content of zinc, around 5%, of a beautiful yellow colour, although of course it tarnishes. Unlike pure copper, surprisingly, red enamel applied directly can work beautifully on gilding metal. Which brings us to…
When enamelling these metals, we will observe some unfortunate reactions due to the chemical interactions taking place with elements in the enamel. I will be talking about the reactions that happen when we apply colours directly on the metal. To avoid these reactions, we apply a layer of flux as an isolation layer. Now have in mind that when talking about alloys, reactions to all the metals contained might take place, in function of their proportions. Testing is always necessary, and these are just things to keep in mind.
And to test, we make colour palettes. You can watch my free video in which I explain how I make my colour palettes. My palettes are very complete due to the nature of my work, but each enameler adapts these to best serve their purposes. Making palettes is a great beginner project.
As a further note, none of the reactions I am going to talk about apply to opaque enamels. Since they’re opaque, none of the interactions occurring on the interface between the metal and the glass are visible to us. So you can use them without worries.
When you apply red, pinks, yellows and some oranges directly on silver, you get a nasty reaction and the enamel might turn unevenly orange, slightly opaque, or nasty altogether, in a most often quite unattractive manner. There are some exceptions in the red and pink range, very few and far between. So those can be applied directly on the silver.
Opalescent enamels also turn yellow and nasty. Again there are a very few exceptions in this already very small category of enamels.
For this reason, when working with these warm shades and opalescents, an isolation layer of flux especially formulated for silver is used.
Unless a reaction takes place, silver is a white metal and transparent colours will generally appear as they are, unaltered and true.
Nothing reacts to gold! It is indeed a dream metal to enamel on. However, there is no going against the laws of physics. When you enamel on gold with transparent colors, the yellow of the gold will be visible through the glass. Blues will tend towards teal, bluish reds will turn more vermillion or orange, if you want a neutral green you will have to use a more turquoise enamel, etc. You can use a color wheel as a guideline. The real problem is violet, which is the complementary of yellow and most often you will get an ugly color. Again, testing is necessary.
So as we said, copper generates firescale. A good copper flux will absorb it all through a sufficient layer and a good fire at high temperature. However most transparent enamels will not be able to. There will be some staining, opacification, or other effects, which can indeed be interesting. A few colors can absorb all of the firescale, acting like a flux, and will look absolutely beautiful. Intense cobalt blues generally are able to. Other colors that can do this are few and far between. Again, testing is necessary. Unfortunately I have never found a red or pink that was able to (but remember this is possible on gilding metal!), and the yellows that did are not with us anymore, they’ve been discontinued.
For this reason, often flux is applied as an isolation layer on copper.
As a final note, new enamels are constantly being developed, and often surprising effects can be found in the new ranges of unleaded enamels, so keep an open mind for new developments in this field.
Another aspect I am gonna briefly touch upon is the heat source, which we need to fuse the enamels to the base metals. These temperatures typically range between 800 and 1000 degree centigrade. The most controlled way to achieve these temperatures and hold them is an enamelling kiln. These are very insulated chambers with coil elements that heat up through electricity, and a door that can be opened to put the pieces in. In enameling, unlike in ceramics, we place the pieces in the already up to temperature kiln, and the firings are comparatively very short, not hours or days, but just seconds or minutes.
Direct fire, like a jeweler’s torch, can also be used to fuse the enamel to the metal. The flame is typically applied form below, since it will blacken the surfaces it touches. This is a bit more difficult to control and used in smaller items that do not require exacting precision.
In the past enamellers also used gas kilns, but these have been replaced with electric ones for convenience.
Techniques and a little history to go with them
Let’s have a quick look at the traditional enamel techniques that have been developed throughout the ages. You can see the images in the video at the top of this post.
Let’s go through them in approximate chronological order. You will notice how enamel was at first mostly associated to jewellery, and the fields delimited by metal cells or walls, the enamel often trying to imitate precious stones, and gradually it gained more and more independence, until whole paintings, with no cells, were created around the renaissance.
The oldest enamel proper, fused directly onto the metal, we find in the island of Cyprus, approx. 1200 BC. Six rings were excavated from a late cypriot tomb and they’re the oldest true enamels that we have found to date, and they’re made with cloisonné technique.
Cloisonné consists of application of enamel separated by cells made out of thin wire. This wire can be fused or soldered to the base metal or just melted onto a previous layer of enamel. The cells are commonly filled to the top of the wires and then the whole sanded level, but not always so, for example on hellenistic jewellery we sometimes find enamelling among the filigree and granulation, and the cells are not filled up, unfortunately the enamel in these has often chipped.
In the east, we find an impressive and old Chinese tradition of cloisonné, and also in Japan, with exquisite work being made in the Meiji period, and also beautiful examples of Indian cloisonné.
Interestingly, the second technique we can talk about is ronde bosse. Look at these wonderful examples of hellenistic and etruscan jewellery with swans and roosters enameled in white. Ronde bosse is the application of enamel onto a three dimensional, sculpture-like form, and it is a very challenging technique. It was also big during the middle ages and the renaissance, and to an extent also during the art nouveau period.
Let’s now talk about champlevé. This technique seems to originate with celtic tribes in the north and west of europe and britain.
The roman examples from around the same time are also found in gallic and british regions so there seems to be a clear link. Champlevé is a technique where we excavate cells into a solid field of metal, and fill these with enamel, generally up to the level of the metal. This technique continued to be popular through the middle ages and beyond in areas of celtic influence, both in jewellery and sacred art, the most famous and main manufacturing centre for this type of work was Limoges in france, with other regions in Europe following suit through this time. So much of this type of work was produced throughout the romanesque period, the early middle ages, that you will find examples in nearly every museum.
Next, Basse taille! During the medieval gothic period (so the latter middle ages) we see the development of transparent enamels for the first time. Since now we can see through the glass into the metal below, the natural evolution of the champlevé technique is to engrave the metal before enamelling, and we call this basse taille, low relief, and you will very often see it combined with champlevé, sometimes only to protect the edges, sometimes as part of the design. At this time we see the production centers move to Sienna and Catalonia, and the enamel work is done over engraved silver. There’s a beautiful depth to this technique.
A subset of basse taille is the technique of guilloché, in which the metal is engraved by a machine, called a rose engine lathe, in beautiful moiré patterns.
This technique was developed to use on metals and then enamelled on top in the 18th century and was used extensively through to the 20th century. A very popular example are the eggs, cigar boxes and other luxury objects created by Fabergé for the russian court.
In the evolution towards the Renaissance we go towards the painted enamel techniques. Enamel divorces from jewellery and metalsmithing for the first time and we see the first independent panels, paintings made with glass, without any metals to separate areas of colour. Within this wider umbrella we can identify painted enamel proper, in which only regular vitreous enamel is used, painting over enamel (often called miniature) in which onglaze pigments are used (onglaze pigments contain more oxide and less glass, they are finely ground and a lot of detail can be achieved) and grisaille. Grisaille is developed around 1530, with the best examples coming from Limoges. In this monochrome technique light enamel is used in layers on a dark background, modeling body anatomy and portraits in exquisite gradations. There are also wonderful examples of this technique in the 19th century, and more recently the variation developed by Andreu Vilasis, using opalescent enamel. I have published a video class detailing this latter technique which you can find at enamelworkshop.com
The technique of painting over enamel, or miniature, was greatly developed during the 18h century, when little luxury objects like boxes and watches are enamelled with exquisitely detailed portraits, court scenes and mythological themes.
Finally we arrive to plique a jour, which was reportedly developed before the 19th century, but surely comes into full bloom during the art nouveau period. With plique a jour we fill cells with enamel, without any backing, and the result is like a miniature stained glass, the light going through the enamel. There are countless examples of this technique being used to best effect and at the highest technical level during this period. Enjoy a little selection.
And these are the main enamelling techniques. There are of course multiple combinations and sub-techniques, but I do hope this little guide will help you identify them and choose the technique that better will translate your design and artistic vision.
More at Enamel Workshop
Browse this website to find my video classes that you can purchase to learn more about this art. You can begin with my class on shaping metal bases and preparation and follow up with the wet packing and gradations class. Many more classes will be arriving soon, make sure to subscribe to the newsletter to never miss a new release.
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There are many books about enamelling out there, and each enameler will have their favourite. This is the one I like to recommend to beginners and intermediate enamelers, written by Núria López-Ribalta. It is very accessible and also very complete, it covers all of the areas I covered in this article, and more. Best of all, it is available in a lot of different languages, and it is affordable and easy to find in online stores.
Non-affiliate links to purchase the book:
English: Emaux Soyer, Bookdepository, Amazon.com, Amazon UK, Amazon DE
Spanish: Emaux Soyer, Amazon ES
French: Emaux Soyer, Amazon FR
Italian: Amazon.com, Mondadori, Hobbyland, IBS
It begins with a very complete chapter on history of enamel, and it is wonderful since Núria is also an art historian. It continues on to a chapter on the enamel material itself, and then on to other materials and tools necessary for enamelling before moving on to the technical processes, techniques and beyond. Highly recommended!
Read more about recommended books in this blog post.