Silver Plated Steel, according to Thompson Enamel catalog is: “Jewelry
grade pieces with fine textured surfaces. Ideal for transparent
enamels. All pieces are slightly domed.” You can order various shapes
in various sizes. This is the sole description & the pieces come with
NO instructions. The recently published "Thompson Enamel Workbook"
expands to a whole paragraph on page 14, which in most part reads: “…
provides the strength of steel to prevent warping during firing and a
surface which is excellent for transparent enamels. … We caution
about too much aggressive cleaning and pickling which might remove most
of the silver plating. Also, firing temperature should not exceed 1450F
and the number of firings should be kept to a minimum.”
I can agree with the above paragraph in all ways. However, it does not
go very far in explaining how to use the product. Through much trial,
error, destroyed pieces & a reply to my letter a few years ago, there is
much more to be said.
The plating of silver reacts much the same with lead free enamels as
does fine silver. Any of the cadmium/selenium colors will darken with
repeated or prolonged firing & transparent colors can turn opaque as a
result of chemical interaction with silver (or even copper). My
experiences & nuggets of guidance from Tom Ellis follow.
I use 200 mesh 2020 clear for silver as the base coat over both sides of
the SPS. Colors will work (excepting the cadmium/selenium group or gold
bearing colors), but I am going to Cloisonn over this base, so I use
clear. I gently clean the metal with soap & water. Dry it immediately,
as rusty spots have been known to occur. The rusty areas may or may not
come out with re-cleaning or in the presence of heat. I then sift 2020
over a fine spray of a 50/50 mixture of Klyr Fire & water. Let it dry.
Tom suggested the first coat should be applied to the front of the
piece, rather than the counter side. My process is sifting over both
sides at once, drying between sides. This gets you one firing ahead of
the game on a surface which may not stand more than 6 firings total.
Fire this first coat fairly close to the 1450F maximum or the 2020 has a
tendency to yellow ( & remain so!)
If I am planning to use cadmium/selenium or gold bearing colors in my
design, I will add another clear coat to both sides & fire. Then I
place my wires, fire again & go on from there. If only a few areas will
receive the problem colors, I wire after the first firing, fire & then
add more clear in just the areas to receive those yellows, reds, etc.
Thompson’s “Workbook” lists all the affected colors by number.
Because you fire at lower temperatures, some transparent colors may not
fire truly clear. Some of the colors I use, Thompsons Oil Gray & Elan,
really don’t fuse completely unless fired at close to the maximum
temperature.
The problems that occur when you go above 1450F have been the formation
of bubbles at the surface of the metal. Also, you may get that eutectic
problem, where the silver cloisonn wires may melt, having come in too
close contact with the base metal. Stoning before the last firing must
be done very carefully & you must absolutely make sure all the grit is
washed out & the piece is clean. I never pickle these pieces! The
edges must be looked after, every firing. You can’t file with a heavy
hand or damage will be done which I have not figured out how to fix.
You can of course bezel the finished piece. SPS can’t be soldered upon
at all! I have yet to figure out an elegant method to attach a pin back
for a brooch. I don’t have a Sparkie, but it may just be possible to
fuse in this case, where you can’t solder. I don’t know. Does anyone
else know? My best stoning technique is using diamond files & diamond
sanding sticks, rather than alundum stones. The cost of SPS is not
cheap! It is comparable to using fine silver.
Why use such a picky material at all, you may wonder. I like the fact
that the pieces come domed & when using ovals & circles, nothing beats
the regularity of a machined shape. I have found no supplier for fine
silver that (a) domes the circles (b) cuts ovals (domed or not). The
circles come in larger sizes than I can get suppliers to cut, 2 1/4" & 2
7/8". If carefully handled, the edges need no finish. The SPS is a
much lighter weight for its size than copper or silver. Very thin
copper & silver has drawbacks when doing Cloisonn. I like the
texture of the SPS. And it was worth the effort to learn to use SPS,
until such time as I become a much better metalsmith. No fire scale to
contend with.
So, in case you ever wondered, now you know a bit more. As always, just
my humble opinions or experiences & I welcome additional
Eileen Schneegas
@D_A_Schneegas