Mike, you can safely reduce the viscosity of 510-Pyro and other developers mixed in TEA by adding some warm (80 - 100 F) Propylene Glycol to the mix.
Can you say more about this? Do you cut the stock made with TEA with however much P.G. and factor that into the dilutions?
IE: 400ml 510-Pyro + 400ml P.G. then 1:50 for 1:100 dilution
Does the P.G. have any effect on keeping qualities?
