Rattlesnake skin redo

I am trying to "retan" a rattlesnake skin. It is old and "crispy", no telling what kind of tan was used, if any. I tried a small test patch using snake tan, the blue liquid. Seems to have soaked in, but hasn't loosened it up as I had hoped.

Any ideas on what to do next ? more snake tan? soak it in ?!?

The end desired result is a flat skin pinned and/or glued onto a backing board that will be framed.

Thanks,