By Dorothy Cockrell
(With permission from the author. This article appeared before in the journal of The Guild of Enamellers.)

Those who teach enamelling to school-children and older students are advised to use lead free enamels, but many remain to be convinced they are as good as the leaded variety - especially in the case of yellows and reds. Having taken part in a workshop on Plique-à-Jour given by Marek Kropelnicki at the 1997 Guild of Enamellers Conference, and being also in possession of a sample set of Thompson's enamels, it seemed appropriate to put the two together.

Thompson's catalogue gives colour illustrations of the effects of using their enamels on silver, copper, gold and gilding metal, but does not indicate the pure colours. Their melting point seems to be below that of leaded enamels (about 700 - 750°C), so there could be an advantage in using them on silver - it's only too easy to concentrate too hard on firing the enamel clear and forget about the melting point of the silver!

I considered making samples on mica - without any metal frame - but decided to use silver frames to test for a reaction, especially in the case of reds. All samples were done by the suspension technique to ensure that no mica could adhere and change the colour of the enamel.

The frames were made using 0.9 mm thick standard silver with three holes: 2 mm, 3 mm and 4 mm in diameter. This gave a variation in tone - enamel in the smaller holes being darker than that in the larger. The sample enamels used were 80 mesh powder, but lump form, which ought to give a greater clarity, is available from Thompson's.

The code numbers for the enamels indicate their depth of colour. To quote from Thompson's catalogue: "All enamel products in this catalogue are numbered into a practical code numbering system which indicates enamel type and colour. The 'thousands' number indicates enamel type while the 'hundreds' number indicates the colour. The final two numbers indicate how light or dark that colour is." I wondered if it would be possible to judge the suitability of any particular colour for plique-à-jour simply from its code number, but it transpired that the code number is useful within a particular group of colours (and anything up to 30 is safe), but many higher numbers were good in certain groups.

When assessing their suitability for use in plique-à-jour, I looked for good colour when held up to the light, and in the case of the reds, no yellow line where the enamel touched the silver frame. Where the report says: 'maybe', the colour is a 'touch' dark, but might be suitable in a larger aperture where more light would pass through it. 'Fair' indicates that - in my opinion- it could be used in a large aperture if you want that colour, but it is a touch dark or dull and would not be a first choice.

I found the powdered enamels as easy to use as leaded ones and felt more confident about leaving samples in the kiln until I felt sure the enamel was completely molten - there were no disasters with the silver!

Many of the colours were lovely, especially the blues, greens and golden browns. As I expected from the limited number in the catalogue, the yellows were less interesting. Soft yellow (# 2210) was too pale for this purpose, egg yellow (# 2215) was pleasant, and the greenish yellows (# 2220, # 2222, # 2230) were good but similar in tone.

There are more reds to choose from, some bluish, some orange, and one glorious red (Woodrow red # 2880) which unfortunately is a bit dark for plique-à-jour. Three had no yellow lines where they met the silver frame - pale pinks # 2820, # 2825, # 2837 - also the red # 2880. In plique-à-jour they mostly came out as pink rather than red until the number # 2840 was reached. None of the yellow lines were serious, one had to know to look for it.

I made no attempt on this occasion to compare colours with their nearest equivalent in leaded enamels. My purpose was to try them for themselves with no metal backing to alter the colours. A future project will be to compare lump form lead free enamel with the same in leaded colours, as that is what I would normally use for plique-à-jour.

Testing Thompson's Eamels for Plique-à-Jour
(All samples done on sterling silver - 0,9 mm thick.
Sample size: 1,5 cm x 0,75 cm, 3 round holes drilled: 2 mm, 3 mm, 4 mm, in each sample.)

Powder enamel as supplied in samples from Thompson's, ground and washed to fine sugar density. Applied with a fine paint brush, suspended in the holes. No mica used. Fired to sugar stage and then refilled as necessary. Generally three applications were necessary to fill the holes, all fired concave.

The kiln was a flamefast Mini Kiln - gas fired with no temperature control. It seems to operate at about 800°C. It's good for plique-à-jour because there is a space at the top of the door which allows exact judgement of the stages in firing.

Since writing the article above, I have obtained some lump enamel from Thompson's and used it for two pairs of earrings. As I expected, the clarity seems slightly better than with the powdered enamel and I am very pleased with the results. I think they may not be as acid resistant as the leaded enamels - after 5 - 10 minutes in Safety Pickle they had a dull 'skin' on the surface which took two firings to get rid of. In future I will not pickle after firing.

Click here for the testresults per colour.