We do not make a liquid grade and dry it down, but it is made as a precipitate, then filtered and dried. Dry powder ferric oxalate has a very long shelf life. I still have some that I made in 1984 and it is still bright yellow green and in perfect condition. Many top printers depend on this consistency. Some of the best platinum printers in the world today use our powdered version and make perfect prints.
Some printers make some modifications to the base product, others use it straight.
The best magic we can see is for the ferric oxalate to be stable and consistent from batch to batch and then let the printers make their own modifications to it if they wish. Powdered ferric oxalate will last a long time and can be quickly put into solution. This will clear up any slight content of ferrous oxalate to ferric oxalate, and will act as a long term preservative. Some outgassing may occur with the use of peroxide, and vented cone caps should be used so the bottles do not explode. Though we have heard of no reports of this happening, we don't add peroxide to our liquid grade products because of this slight risk.