Quote Originally Posted by T-grain View Post
...I am afraid these PVA matrices simply won't work. The reason is simple: they don't have the amino groups present in the gelatin. The dyes (in their ionic form) are attracted to the protonated amino groups (gelatin), so that's why they are held in place even when you rinse the matrix in acetic acid solution. When you make the contact with the receiving paper, there is a gradient in pH between the matrix and the receiving gelatin, so the dye molecules are driven there. Simply put, the dye molecules are more attracted to a gelatin environment with pH 6 rather than about pH 4...
This sounds like a very good assessment of the situation, specifically regarding the amino groups. Not something I know much about, but definitely, the DT mechanism relies on a special relationship between certain types of dyes & gelatin protein.

And regarding,
I thought a Thorium salt was needed just to enhance sharpness not to actually hold the dye in the receiving gelatin?"
That is certainly my understanding as well. I've transferred magenta dye to a fixed-out (non-hardening) FB paper and the density is very good, but diffusion is terrible! The mechanism of imbibition though, relies on this pH gradient and not a mordant.

Speaking of which... you can buy thorium nitrate on eBay for fairly low prices. Not that I'm even considering such an endeavor..