I refer the honourable gentleman to my answer of 26th June..... AIUI, emulsions such as C41, E6, and ordinary colour print papers have the dyes synthesised not in a chemical factory, but in situ in the emulsion during processing. 'Colour coupler' molecules in the emulsion and the oxidation product of the colour developer link together to give a long molecule with the desired colour. This is a remarkably clever bit of chemistry.
In contrast, in Kodachrome and Cibachrome processes the dye molecules are presynthesised in one piece. In Kodachrome they are diffused into the emulsion during processing, and in Cibachrome, the unwanted dyes are selectively bleached out during processing. It is thus inherently easier in the latter processes to use permanent dyes; the colour chemists have fewer constraints because they don't have to meet the requirements of developer chemistry as well as everything else. Regards, Alan Tyson ----- Original Message ----- From: Rob Geraghty <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, December 14, 2001 12:05 AM > I've heard that too, although I don't understand what difference it makes > when the dyes are added! > (but I can see that it does) > > Rob