I have made up direct selenium toner in the past, with great care, under a fume hood (well, immediately adjacent to the exhaust intake to my HRV that draws at the end of my sink where the fixer tray usually sits) running full blast.

Heating the mixture of the very finely divided Se powder and getting it into a sulfite solution, then heating it, all the whle in nitrile gloves, and wearing a full mouth and nose filtered respirator was a real pain in the ass.

After that first effor I had a few different lots of of KRST come my way. It will be quite a while before I consider mixing selenium from scratch again.