[srs5694]

Mr. Gainer should have chimed in. He is a proponent of the least toxic combinations of developer chemistries for both film and paper.

Three chemicals are needed; phenidone, ascorbic acid, and borax.

I don't recall Pat Gainer posting, but I did mention the two commercial PC (phenidone/ascorbic acid) developers I know of: Agfa Neutol Plus and Silvergrain Tektol. Mixing a developer yourself vs. using a pre-mixed liquid developer does add to the risk, since you'll then have powdered chemicals floating about. OTOH, I doubt if many people would give a second thought to mixing powdered vitamin C into a drink or using any of the many powdered detergents that contain borax or sodium carbonate.

Phenidone is so little toxic that it need not be mentioned in MSDS sheets.

I'm not sure the issue is entirely a matter of phenidone's toxicity; I think it's at least partly because phenidone appears in such small quantities. A typical PC developer has about 0.1g of phenidone per liter of working solution, or proportionally more in a concentrate. I've seen many MSDSes that include notes to the effect that substances at under a 1% concentration are omitted. There's about ten times as much metol in a typical MQ developer, by comparison.

That said, my understanding is that phenidone is among the least toxic of the common B&W developing agents.