Well, having read over the years many times to use a @ 0.1% solution, I took to my books for a definitive answer.
So prepare to be educated / even more confused than ever...
First, the
Darkroom Cookbook, which says:
'Mix a 0.2% solution (2 grammes in 1 litre water at 125F / 52C or higher). Add 15.0ml of this solution to every litre of (
working strength) developer. If 15.0ml does not do the trick, keep adding 15.0ml at a time... until you get a clear paper without a fog. A little experimentation will be required.'
Note that it doesn't give a maximum amount that can be added, but general reading says that adding too much will introduce even more fog.
Secondly
Ansel Adams,
The Print states that he uses a '1.0% solution, adding 25cc to
stock developer solution.' It says that 50cc produces a noticeable blue colour shift of the paper and 100cc reduces paper speed by about 2/3 of a f-stop.
Thirdly and last is from
Tim Rudman's Master Printing Course book:
'Benzotriazole 1%. 5ml in 1 litre of
working developer. Expose to the shortest recommended development time and then experiment to ensure maximum blacks.'
Also recommended in his book and else where, is the use of potassium bromide 10%; using 10ml in 1 litre of working solution.
Note that bromide gives a warmer image compared to a cooler one with benzotriazole.
Hopefully this will all be of help and the bottom line seems to be to experiment a bit.
Terry S