It's a very expensive, reagent wise, to make 1 little varnish. A failure at you lose 3 precious reagents, or if by horror you only have 2 left, you are stuck carrying them around until you have another. It's time and space and weight allowance consuming.
My suggestion is that on failure, you only lose 2/3 of the reagents, or 1/2. It would lessen the amount of farming done in order to raise a few levels in the craft and less frustrating to lose 3 reagents.