Opaque white enamels in contact with silver
By Mer Almagro, March 2022
Just as opalescent enamels, opaque white enamels tend to develop a brownish chemical reaction when they come in contact with silver. Opaque enamels are rarely applied on top of precious metals in a painted enamel context (since they entirely obscure it, copper is often used instead); however they are often used in contact with fine silver cloissons (wires) in the cloissoné technique. This article aims to help counter this effect when this is the case.
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As all such reactions to silver (also seen in most warm transparent enamels such as reds and yellows), they are due to metal oxides being taken in solution within the enamel glass while the enamel is in a fluid state: while being fired in the kiln. Thus prolonged and/or repeated fires tend to increase the severity of the reaction. A first line of defence against this effect is then to limit the amount of time in the kiln by:
- planning the layers needed to create the work to limit the amount of firings necessary
- whenever possible, firing only to orange peel stage to limit time in the kiln
- increasing the firing temperature so that the firings can be as short as possible
That being said, it is always wise to choose of a particular white enamel which displays less tendency to brown when in contact with silver. For this reason I’ve created the following test with the opaque white enamels we have available in the store, and a few extra others as a point of comparison. The enamels used:
Blythe T1, T6, T7; Soyer 148 (discontinued), 160; Schauer 201, 202; Milton Bridge ODW1, 141
Note: on the palette above, I superimposed the colour numbers. To see the original image of the palette click here. To see the full size of the above image click here. Side view here.
My conclusion from this test is that I would choose Soyer 160 or Schauer 202 for this application. Further:
- This was a somewhat surprising result, as I expected the harder white enamels to take less oxide in, but the conclusion is much the opposite.
- 160 and 202 are the softest enamels in the lineup. Whenever a softer enamel won’t interfere with the layer planning of a piece, these would be my choices.
- If a slightly harder enamel would be advisable, I would choose Blythe T7 or Schauer 201.
- If a hard enamel is necessary, with careful firing and planning you can also use Blythe T6.
- None of these enamels need isolation from the wires with flux. Flux in fact did either not seem to have much influence and in fact in most cases created extra problems. Blythe C1 (a softer flux) performed better, and Soyer 3 (a hard flux) worse.
I consider this palette to have received a normal amount of firings and layers: two layers to reasonably fill the cells, firing to orange peel; another layer plus stronger firing to assess how much enamel is still necessary to entirely fill the circles and to allow all whites to properly stick to the wires; a fourth layer to fill up gaps, followed by a measured fire and grinding down level; followed by a final, careful gloss fire.
A few more notes on the process are given further below, but for mored detail here you can find my Patreon video about the process and reasoning I followed. In it I go into a lot more depth and nuance than I possibly could in this article. You can learn more about my Patreon subscription service here. Please do not assume this to be my first tutorial on cloisonné, since I focus on the reasoning behind a useful test palette, not the technique itself. That will be upcoming as a class in the future.
I wanted to take this test further, push the white enamels to their limits. Thus after this test, I fired the palette again, for a long time, until I noticed some wires were beginning to sink (probably the beginning of a eutectic melting into the copper, which I cannot observe directly due to the opaque enamel – you can see that better in the Patreon video). This is the result:
The numbers are in this case vitrifiable paint fired in place. Click here to view full size.
More defects and discolouration of course appeared due to the very prolonged fire. This provides further information which can help choose the right enamel for any particular application. I would of course always advise against firing a piece in this way!
I would also advise against using ODW1 in cloisonné pieces or other techniques in combination with other enamels as it exhibits a tendency to cracking. It is a white watch dial opaque that is best used on its own, and suited for that purpose (painting on enamel).
More process notes
I applied fine silver cloissons on a layer of Soyer 1 copper flux fired on top of copper. I also applied both Soyer 3 silver flux to the top half of both the inside and outside of the wire on the larger circles, and likewise Blythe C1 gold flux to the medium circles. The purpose of the flux is to test if this strategy helps isolate the white enamel from making contact with the silver. This image illustrates the positioning of the fluxes (dry, before firing to gloss):
After firing the flux, I applied the white enamels between and within the cells, in four layers up to the level of the wires.
Up to the the last, prolonged firing test, the enamels were always fired for the shortest time possible. Since the different whites have different melting points, this means some were molten to gloss while others went barely past sugar coat. For more information on the precise process followed, watch my Patreon video.