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Enamel techniques

Enamelling, whichever the technique used, always involves a close communion between enamel and metal. The latter, forming the support, is entirely covered in the case of painted enamel, which will be studied later, and it can only be detected by transparency.
The techniques called champlevé and cloisonné enable the metal to widen its role. From simple physical support, but hidden like a canvas, it becomes visible and becomes part of the composition, like the colour.

Champlevé

The metal generally used is the copper. The necessary plate, flat or shaped according to the object to create, requires a minimum thickness of two millimetres. The drawing, finalized beforehand with great care, is transferred with a hard lead or a dry point. The fundamental principle being to fill the enamel in designated recesses, then takes place the key phase consisting in creating these recesses.

The chisel and the etching needle are naturally designated for that, and when the tool has reached a depth in the order of half a millimetre, it will define the edges, the quality of which is deciding for the future aspect of the work.

The artist can also paint with an asphalt lacquer the metal parts to save and plunge the piece in an acid bath, which enables to trim the recesses with a large surface. The lack of precision of the etching requires however the intervention of the etching needle as far as the size of the edges and of the recesses with a small surface is concerned.
The enamel as a wet powder is then applied with a spatula in the recesses. The quantity to apply will cover the metal parts in relief, the role of which is generally to separate different colours. The process becomes very tricky in the case of small ribs (a tenth of a millimetre in width for example) because colours overflowing is not good in the usual champlevé.

After cooling, the enamel surpluses are removed by an energetic sanding with a hard stone and water. So metal reserves reappear and finer and finer abrasives finish the process.
In a classic champlevé, we are looking for a perfectly smooth aspect of the surface. It is achieved with an insistent rubbing of the piece with a rottenstone for example.
According to the requirements of the model, the etching needle and the chisel intervene again on the visible parts of the metal to chisel, etch and chequer, as many effects that will brighten up the surface and catch the light.
The copper is unfortunately not stable, hence the need to protect the piece against oxidation. It is achieved in most of the gilding cases. The best results are the ones achieved thanks to electroplating which enables, on demand, a gold deposit of variable thickness and aspect.

Cloisonné

Close to the champlevé as far as the aspect is concerned, the cloisonné is like the champlevé and an undiscerning eye often mixes them up because in both techniques, the metal is partly visible in the piece design.
The personalizing detail comes from the way the recesses are made :

- The champlevé works by ablation of a part of the metal.
- The cloisonné adds parts.

The drawing is transferred on the plate like with the previous technique. Then a thin strip of copper, gold or silver is shaped by folding with pliers until it takes on perfectly the arabesque of the line. There are two different ways to fix these cloisons on the support :

- on the bare copper and with a silver solder
- on the previously glazed copper, that is to say covered with a thin layer of colourless enamel.

They are then glued with gum tragacanth. A low firing (the enamel starts to melt) gives them a sufficient adhesion.
The strips thickness varies according to the enamellers: rolling, hammering, stretching enable to reduce the wrinkle effect which would appear with cloisons with a uniform thickness.
During the colouring, a great precision is required for reasons similar to the ones that govern the champlevé, each cloison must clearly separate two interpenetrating shades.
The process is then similar: firings, successive sandings, potential gilding because the small quantity of filler metal enables the use of noble metals, stable like certain silver and gold alloys.
The principle of the partitioning involves a very linear drawing, which enables to distinguish it from the champlevé where the metal reserves take on much freer forms. On the other hand, relatively deep recesses (from 1 to 2 millimetres) are achieved more easily: it enables to use a gold foil or a silver one, that is to say translucent metals, on certain areas, contrary to the champlevé where the opaque enamels dominate.
To shape a design, to fix it, to apply the enamel requires a very long execution time, and the cloisonné, for that reason, does not work well on big sizes. On the contrary, it is the undeniable servant of a certain goldsmithing, delicate and intimate.
 
The painted enamels : technique used by  Jean-Paul BOUCHAREL (Enameller in Limoges)

Translucent enamels

Preparation of the plate :

We use a copper plate of 3 to 5/10th of a millimetre domed with agate or hammered in order to harden the copper.
This process makes the plates domed and is absolutely essential. Indeed, a thin plate which will undergo ten to twenty firings at eight hundred degrees may lose its shape during the manufacturing. Hence this hammering which hardens the cooper and gives this domed aspect to the plates.
This plate is then stripped with acids so that the copper is left perfectly clean and not greasy. Once dry, we sprinkle a thin layer of enamel called flux (we do that with a screen). This plate is passed through a furnace until the vitrification of the enamel and its adhesion to the plate (three to four minutes at 900 degrees).
We repeat this same process to overload the plate (then we can change the temperature to more than 1000 degrees). In this case, the whole "enamel-copper" is subjected to this temperature and the enamel protects the copper. Once out of the furnace, the plates are easily malleable and can be reshaped on a surface plate.

Drawing - Trace

On the plate, prepared this way, we can:
- either paint entirely with a brush with some vitrifiable colours the pattern we want to make
- or cover the piece with a sheet of silver paper (called silver foil) crumpled beforehand (because of the dilatation) and perforated (in order for the air bubbles to escape). This silver foil is passed through a furnace. Like before, we make a trace.
The aim of this process is to create an optical screen without colours in order to obtain enamels not influenced by the pink tinge due to the copper in transparency.

Enamelling - colour

The matter used - enamels – comes as wrought sands always wet and kept under water (to avoid dusts). The working tool: the spatula.
The different colours of the enamels come from metal oxides mixtures, grinded with the different silicates. These different metal oxides constitute the palette of the enameller and will influence his/her work so particular, because:
- at 15 degrees an enamel has a certain colour, at 800 degrees it will change colour and oxidize when taking its final colour, which requires a transposition
- each colour, to reveal itself to a maximum, will pass through a furnace, the temperature depending on each colour. So, numerous firings are necessary, starting from the highest temperatures and we must be familiar with our palette to mix the only colours that can be translucent.
For the flowers and the landscapes, the painting is nearly finished.
 
White painting (Limoges) - grisaille

For the subjects, the most delicate part begins. Indeed, at this stage, the faces, the hands, the laces, etc… have been treated like the rest and are very hazy. The edges are uncertain and the whole piece lacks some light and gradients.

We will now conduct the travail de blanc, technique finalized in the 16th century, which will give its fineness to the enamel. The matter used (Limoges white) in an enamel very finely grinded with heavy vegetable oils, which gives a very thick white paste. The instruments: two or three yarn brush, needle mounted on a wooden handle.
With the brush, we put a little bit of this paste on the part we want to light up. This very thick paste does not “follow” the brush and each brush stroke is visible. Then, we stretch this paste with a needle, creating a real modeling. This work is what will give their fineness and shades to the enamels.

When the plate is covered with this extremely thin white film on the desired areas, it goes in the furnace at 500 or 600 degrees. The enamel is vitrified.
It should be noted in passing that the temperatures required to fix and vitrify this white are far lower than the other firings. An excess fire destroys the travail de blanc which disappears, leaving only a yellow residue. We then start again as many times as necessary to obtain the desired effect, renewing each time the needle work.

By superimposing these layers, we can obtain all the desired shades. Generally, three to four layers of white are necessary, even if the piece is very small.

The grisailles

The part we will work on with the Limoges white is left in black enamel. The work with the white is then done with a needle; it requires two, three, four, sometimes five successive layers, each time passing through the furnace and with a vitrification. The achieved result is a gradient of greys which “sculpts” the surface we worked on. This is by far the most delicate work in this technique.

Opaque enamels

The preparatory fires, the drawings and paintings are the same, although it is not necessary to paint the plate, we just need to make a line drawing.
The enamelling is made in one go, two at a maximum, because the colours cover the previous ones. For example, if we put blue on red, we have blue. The red is completely covered, whereas with translucent enamels, we had a component of both colours (purple in this case).

Sometimes, we can repaint the opaque enamels to soften the solid tint prints. The firings are made at far lower temperatures, either 400 or 500 degrees.
Of course, all the variants, consisting in combining opaque enamels, translucent enamels, firings too strong or too gentle, exist...

At this stage, the technique – necessary of course – leaves room for the imagination.