The thing about clearing is that you need enough and no more. And every paper is different. For instance Rives BFK is a beautiful paper, but a real bite in the butt to clear. In contrast, Cranes clears very easily. The point being that you need to experiment a little bit and figure out what concentration and time you need to adequately clear any given paper. I used to mix up a home brew hypoclear as follows:
1 teaspoon sodium bisulfite in a liter of warm water and stir until dissolved, then
1 tbsp of sodium sulfite
and then
1 tbsp of EDTA.
This would generally clear COT320 with three five minute baths.
It is advisable when you are first using a new paper to mask the border and check your clearing by holding your paper up to a light and seeing if you can detect residual ferric oxalate. There is also a chemical test that, if I remember correctly, involves adding a little drop of a potassium ferricyanide solution to a supposedly cleared area. You'll have to google that one. I like the visual check.
If it isn't clearing, check the pH of your clearing baths. If they are above 7, you are just pissing into the wind. Some stubborn papers may require a first bath of phosphoric acid or even dilute (1-2%)hydrochloric acid. Just be aware that if you throw a piece of paper that has spent five minutes in a hydrochloric acid bath straight into a tray containing sodium sulfite, you may think you have a rotten egg somewhere in your darkroom. So it is a good idea to briefly rinse the paper after the acid bath if you are using a strong acid as a clearing agent. It is not an exact science, as you can see from this rambling post.....
