Quote Originally Posted by mdm View Post
Looking at MSDS sheets it seems some screen printing sensitisers have formalin in them, which would explain insoluble tissue.
Yep...I saw those data sheets. That is not the sensitizer I used, so that can't be the exact problem that I had. But I saw one datasheet that listed the chemical in question as:

Chemical name DiazoniumSalt: p-diazodiphenylamine sulfate, formaldehyde condensate (41432-19-3).
Note: End product does not contain free formaldehyde.
Emphasis mine.

In the thread from the dye transfer list that I linked to, the OP claims to have tested (successfully) a number of different manufacturer's sensitizers, some of which use the chemical above. I plan on testing it if I can get my hands on it (without having to also purchase the screen emulsion along with it.)