If the goal is to generate a reasonably detailed image in a color scheme that
approximates what you want then you have a chance.
At least here in Wisconsin the church graveyards that go back to the start of
the century are full of headstones with an inset photomedallion bearing a very
good image, presumably of the person interred. The ones I recall are all
monochromatic but the techniques involved will support multiple images and
thus color. January is a good time to tramp around in old graveyards here
in the North. You will be amazed at the numbers of young people who died in
the influenza epedemic of 1918. Quite sobering.
The colors will depend on the glaze colorants used and the firing conditions.
Ceramic colors are highly sensitive to a whole bunch of variables. You have a
balance to achieve which cannot be dealt with here.
Wall's Dictionary of Photography, I have the 12th edition from 1931 in front
of me, describes the following choices. I've used or paraphrased the words as
printed with a few comments following in parentheses.
Start paraphrase and assume everything is Wall's words.
1. Substitution. A collodio-chloride printing-out positive is prepared and
fixed. The image is toned with platinum, gold, palladium, irridium or a
selected mixture. The positive is then stripped, transferred to the plaque,
and carefully smoothed out, the fired, coated with glaze, and refired.
(I presume the glaze is transparent. ER)
2. Powder. The preparation of a positive by the powder or dusting-on
process on a sheet of glass, coating it with collodion, stripping, and
transferring to the plaque, and firing.
(There was no mention of a final glaze. ER)
3. Pigment. The pigment process is merely a modification of the carbon
process, gum arabic instead of gelatine being sometimes used as the material;
it is transferred and fired.
(No mention of a final glaze. ER)
4. Collotype. A special ink is used and the print being on litho-transfer
paper, from which it is transferred to the plaque.
There is a description of using multiple collotype images onto an unglazed
tile using a fatty ink containing an ordinary underglaze pottery color. The
tile being then fired and qlazed like an ordinary piece of pottery.
(I presume a transparent glaze here. ER)
End paraphrase.
The plaques appear to be copper enameled ovals with the surface described as a
very soft milk glass. If that is the case then firing at most ceramic
temperatures would utterly destroy them.
It also seems that the powders, pigments, etc. used need to be ceramic
colorants of various types.
An old friend of mine who I have not seen for several years did a large number
of ceramic photo pieces using photo silkscreen to deposit glaze materials onto
the ceramic and then firing. If there is enough interest in this I can try to
contact him again and see if he will elaborate on his techniques for the
group. Years and years ago I worked for a scientific glassware manufacturer
and we put various scales and logos onto the glass with silkscreen and then
fired the stuff in an annealing oven.
I am sure that you will find in your own locations one or more shops selling
hobby ceramics. They will have a wide selection of low temperature
underglaze materials and the final glazes for experimentation. It is likely
that they will also do the firings for you. There is a whole subculture of
people who paint on ceramics. Some with ordinary paints and some with glaze
materials. You may want to use the materials from this latter group.
I think I remember discussions of all of this in ceramics books but I cannot
be sure.
This could be the start of years of happy experimentation.
Good luck.
E. Robkin