Peter, I can now answer your question with a more firm no! I made a sensitizer by mixing 2 parts of a casein/pigment mix with 1 part of a 3% DAS solution. With this mix I prepared 1 sheet of paper and dried it for 30 min in the dark at 45% RH. After this it was exposed with a step wedge for 1 minute under a bank of UV TL. It is 'developed' in water at 20░ C for 30 minutes.
The rest of the mix I kept in the dark at room temperature for 1 hour. After 1 hour I prepared another sheet and also dried it for 30 minutes at the same conditions as the first sheet. Exposure time and wash time were the same as for the first print.
No visible difference can be seen between the two prints! I will examine them with the densitometer when dry, but I think we can safely say the alkaline environment makes no differnce. You may also note that an exposure time of 1 minute is about 4x faster than casein with dichromates. Currently I am also testing synthetic collo´ds. With one collo´d I came in the 5s (!) range for a maximum black.
My casein mix was made by soaking 4 gram of casein powder (kremerpigmente.de) in 35ml water for one hour. After this soaking time 1 gram of ammoniumcarbonate is mixed in and the mix is slightly heated until all carbondioxide is evaporated. I mixed in 2 gr. of lampblack watercolor paint.