Shelf life of thiourea?

[walbergb]

What is the shelf life of homemade thiourea? I mixed up a batch on Wednesday (December 9): 100 gm thiourea + water (purified) to make 1 litre. I will be mixing some fresh sepia toner on Tuesday and wonderinf if its okay to use the thiourea solution or mix a new batch from scratch. I made the sodium hydroxide 10% solution today so that it could cool down by Tuesday (I can't access the community darkroom Sunday and Monday).

 

[Marco Buonocore]

I have found no problems with using 10% solutions of both thiocarbamide and sodium hydroxide for 6 months. I've used them after a longer period of time, but have noticed they start to crystallize. You'll notice the "whisps" at the bottom of the brown glass bottle, and at that point it's probably best to make a new batch.

There may be subtle changes in how the toner behaves, but I don't consider it a big deal. The convenience of using the 10% solutions is wonderful, and is worth this small problem. Perhaps if I was toning a portfolio that needed real consistency, I would make toner up from scratch each session.

 

[Photo Engineer]

Crystalline thiourea is good for years in a tightly closed bottle.

In water it is less so, but IDK how long.

Symptoms of it going bad are similar to hypo. Strong smell of rotten eggs and turning cloudy.

PE

 

[Gerald C Koch]

From my experience teaching qualitative analysis a solution should be good for at least 6 months if protected from excessive heat. We kept a large bottle in the stock room and refilled the bottles in the lab from it.

 

[walbergb]

Thanks fellow apuggers. I'll see what happens on Tuesday.