Post by PeterW on Jul 26, 2011 16:39:44 GMT -5
Hi all,
I recently acquired a DVD of scans of Photocrom (sometimes spelled Photochrome) postcards. They seem to have been scanned from undamaged original postcards Some of the scans are higher resolution than others, but they are all sharp up to postcard size or a little larger.
The process was quite involved. It was invented in the 1880s by a Swiss chemist and involved first hand colouring the black and white negatives.
The rest of the process was basically lithograph printing, and the following description of it is from Wikipedia.
“A tablet of lithographic limestone, known as a litho stone, is coated with a light-sensitive coating, comprising a thin layer of purified bitumen dissolved in benzene. A reversed half-tone negative is then pressed against the coating and exposed to daylight for a period of 10 to 30 minutes in summer, up to several hours in winter. The image on the negative allows varying amounts of light to fall on different areas of the coating, causing the bitumen to harden and become resistant to normal solvents in proportion to the amount of light that falls on it. The coating is then washed in turpentine solutions to remove the unhardened bitumen and retouched in the tonal scale of the chosen color to strengthen or soften the tones as required. Each tint is applied using a separate stone bearing the appropriate retouched image. The finished print is produced using at least six, but more commonly from 10 to 15, tint stones.”
The result was a full-colour postcard years before the development of proper colour photography. They were produced in their hundreds, probably thousands, in both Europe and the US.. Their heyday seems to have been between 1890 and 1905 when there was something of a mania for collecting them.
Here’s a sample:
This is of Portsmouth Harbour, about 1903-05
The Victorians were certainly resourceful and go-ahead.
PeterW
I recently acquired a DVD of scans of Photocrom (sometimes spelled Photochrome) postcards. They seem to have been scanned from undamaged original postcards Some of the scans are higher resolution than others, but they are all sharp up to postcard size or a little larger.
The process was quite involved. It was invented in the 1880s by a Swiss chemist and involved first hand colouring the black and white negatives.
The rest of the process was basically lithograph printing, and the following description of it is from Wikipedia.
“A tablet of lithographic limestone, known as a litho stone, is coated with a light-sensitive coating, comprising a thin layer of purified bitumen dissolved in benzene. A reversed half-tone negative is then pressed against the coating and exposed to daylight for a period of 10 to 30 minutes in summer, up to several hours in winter. The image on the negative allows varying amounts of light to fall on different areas of the coating, causing the bitumen to harden and become resistant to normal solvents in proportion to the amount of light that falls on it. The coating is then washed in turpentine solutions to remove the unhardened bitumen and retouched in the tonal scale of the chosen color to strengthen or soften the tones as required. Each tint is applied using a separate stone bearing the appropriate retouched image. The finished print is produced using at least six, but more commonly from 10 to 15, tint stones.”
The result was a full-colour postcard years before the development of proper colour photography. They were produced in their hundreds, probably thousands, in both Europe and the US.. Their heyday seems to have been between 1890 and 1905 when there was something of a mania for collecting them.
Here’s a sample:
This is of Portsmouth Harbour, about 1903-05
The Victorians were certainly resourceful and go-ahead.
PeterW
