I want to cast a dichromated gelatin photographic relief to make printing plate in the manner of the Woodburytype processof the late 19th century.
I found 1905 reference to it being done with the then newly discovered Spence Metal. I cannot find any reference to the material. I suspect it might be a bismuth lead based alloy. Does anyone have a formula for Spence metal?
--Dick Sullivan
From: F.J. Camm, ed.: "A dictionary of metals and their alloys, their composition and characteristics", London, Georges Newbes LTD, repr.1941.p.
158:"Spence's metal". Strictly speaking, this is not a metallic material. It "consists of a solution of certain metallic sulphides, as, for instance, "those of iron, zinc or lead, in molten sulphur. The "metal" forms a hard, "tenacious, metallic-looking mass of Specific Gravity 3.37 to 3.7. It melts at "about 320°F. and expands on cooling. Is useful at times for making air- and "gas-tight joints in laboratory apparatus, etc."
google finds a link to a "Spence's Metal Manufacturing C°.LTD" which was established in Kent in 1882
...useless but interesting!...
J.J.
From G. S. Brady: Materials Handbook. McGrawHill., 10th ed., 1971, p. 474:
"Spence's metal is the name of an old lute for pipe joining. It was made by introducing iron disulfide, zinc blende and galena into melted sulfur. It melts at 320°F and expands on cooling. It make a good cast joint which is resistant to water, acids and alkalies. It is not a metal."
J.J.
I suspect the expansion on cooling was the valuable part. Originally the gelatin photographic relief was copied by pressing it into a piece of lead. You needed a press big enough to crush a Greyhound Buss to do it though. The Woodbury process was only in use for a few years until other photomechanical reporduction processes proved cheaper, and easier to do. I the later stages other ways of taking an impression were used. One involved pressing tinfoil onto the relief and backing that with a a glue and a sheet of glass. One guy reported backing the tinfoil with plaster of paris and letting tht dry and then coating it with glue, then placing it into a sturdy frame hammered with wedges.The glue.then caused the plaster to swell.
The matrix thus made is filled with pigmented gelatin and paper pressed onto it. The process could beautifully reproduce grainless appearing photographic images in pigment.
I suspect tin foil was used because it wasavailalble. No one makes tin foil economically or in large sizes anymore.
I wonder if annealed aluminum foil would work just as well?
Or is there an epoxy material that swells on setting?
It would also be better to cast the wet relief intead of waiting for it to dry and shrink.
--Dick Sullivan I am a photographer not a material scientists so any help would is greatly appreciated.
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