I made black pigment in November, from lamp soot and the gum, the way my mother used to do it. Kept it in a glass jar with the cloth tied on top. Today I opened it and there is white fur on the surface, a thin layer. First time this has happened to me in so many years.

My mother never had this problem. But she made small quantity, enough for one or two paintings, and it was finished before anything could sit. I made a big batch because a cooperative order was coming and then the order went slow. So the jar is sitting since four months and now this.

Some people will say just throw it. I am not able to throw it, that soot took me three evenings to collect properly, sitting with the diya and the tin plate. I have scraped the top layer off. Underneath it looks fine, black as it should be. But I am hesitating to use it on the order, because if it comes off later on the paper then my name only will be spoiled, not the mould's.

There is an old practice of putting a little neem leaf in the jar. My aunt used to do it. I did not do it this time because I was in a hurry, which is its own kind of foolishness.

Anyone here working with natural pigment, does the spoilage go all the way through or only skin deep. I would like to know before I ruin good handmade paper.