This is not correct.
Originally Posted by Photo Engineer
The base material used for coating Ciba/Ilfochrome was Melinex, manufactured by ICI , is Polyester . Yupo is made of polypropylene and is similar to the Kimdura "synthetic, water proof paper" that was used as a base for coating the UltraStale pigment films.
Polyproplyene should not be used as the final support for carbon transfer prints. Testing has shown it exhibits serious long-term adhesion and cohesion failures.
The white UltraStable base had a gelatin top coat over an in-line gel subbing layer. A receiving top coat is necessary for the long term stability of any prints made onto polyester.
A rule of thumb: if you can transfer the image from a temporary support sheet (yupo, polyester, etc). it should not be used as a final support. You can also test for this by using scotch tape to peel off the processed gelatin image.