If you decide to try it, just try your normal carbon tissue formula, but add 2% - 5% of ferric oxalate to thd pigmented gelatin before you coat. First mix it in water to dissolve, which from memory can be a bit difficult with ferric oxalate. I have not experimented with FO so I have no idea how it will work.

Coat your tissue on a clear polyester sheet (fixed out film, lith tape, etc.) and dry in the dark.

When the tissue is dry, expose through the base. Do not expose directly on the tissue and transfer, this will not work with ferric carbon.

Develop for 2-5 minutes in a 1/2% to 1% solution of hydrogen peroxide, wash for a minute or two, then place in the warm water bath as you normally do with carbon to wash off the soluble gelatin.

It should be possible to transfer the carbon relief on the polyester base to a final paper support, but I have not gotten to that point yet.

I will be interested to hear of your results.

Sandy