Carbon process. Why contact print?

[cinefane]

In carbon process, why is it required that the paper be exposed in contact with an enlarged negative?

Could not an enlarger be used to make the final print, if it were fitted with the appropriate light source?

[Ian Grant]

The Gelatin needs UV exposure via the sun or a UV light source and you would need special lenses for an enlarger with a UV light source. Camera lenses for UV work are(?were) made for scientific use but because they use specialist glasses that makes them expensive.

It's the same reason Silk screen printing needs a UV light source.

Ian

[sanking]

In carbon process, why is it required that the paper be exposed in contact with an enlarged negative?

Could not an enlarger be used to make the final print, if it were fitted with the appropriate light source?


Most alternative processes, including carbon, have very low sensitivity to light. Figures I have seen suggest that the sensitivity of dichromate colloids is about a million times less than that of silver bromide enlarging papers, and thousands of time less than silver chloride papers like AZO and Lodima. This makes enlargement impossible, or at least very impractical, since you would need a light source high in UV radiation of around 10,000 to 20,000 watts.


Sandy King

[2F/2F]

Usually, if something needs to be contact printed, it is because it reacts very slowly to light.