I stumbled on this from the Scientific American 1883: http://www.gutenberg.org/files/11344/11344-h/11344-h.htm#10 Half way down is a wonderful description of the 'new' silver emulsions. It is interesting to see boosterism of Argento-Gelatinate photography in it's infancy - silver gelatin suffering from the same inferiority complex, and presumably, prejudice, as digital does today. I was also intruigued by the term 'Opal', which as far as I can make out means a print made onto opal glass, presumably to be backlit. It sounds a bit like the carbon transfer prints onto ceramic once common on gravestones, but the the 10x12" size and the supporting text suggest that these were for more general display. Do any of the history buffs here know what Opals were used for? I have never seen on in any kind of museum, so have they all broken or am I just looking in the wrong museums? Finally, does anyone make them today? There is a lab in Gothenburg who do colour-carbon onto glass prints, but they don't call them 'opals' or anything like it. Are any of the Civil War reenactment people into this?