You pay our money and take your chances. Of course, ideally, you use the designated thinner (Sig with Sig, Brodak with Brodak, etc) but I've used other stuff. Big thing is don't change in mid-stream. If you start off using Sig Thinner with Brodak dope, do it throughout the finish. Changing in mid-finish will likely create adhesion problems. Somethings you can get away with it but it becomes a "if you hold your head just right and stand on one foot it will work" sort of thing.