Water
From Silvergrain Labs
for processing chemistry
Despite many who believe in distilled water and deionized water, potable tap water is more than adequate for most photographic processing solutions. Most well-formulted processing chemicals are designed to minimize effects from small amount of impurities that may be present in the water.
Tap water may have alkaline pH (the pH of Boston tap water is 9.1 to 9.2 range) and trace amount of minerals and chlorinating agent. The pH is maintained quite high in Boston area to prevent leaching of copper from pipes used in some old buildings. However, the pH is very weakly buffered and it should have no practical influence on well designed developers.
Problem may occur when preparing poorly formulated developers. They are often characterized by:
- inappropriate buffering system
- insufficient buffering capacity
- lack of metal complexing agent
When you have to make these developers, it is probably safer to use distilled or deionized water.
For most applications, I use cold tap water, first filtered to remove particulates, and then filtered with solid carbon filter to remove transition metal cations, much of the chlorinating agents and other organic materials. The pore size I use is 1 micron. The filtered water is gently heated to boiling, and then this water is placed in vacuum chamber (about 600mm Hg lower than atmospheric pressure) for several hours for deaerating. Deaerating process is particularly important for sensitive experimental developers.
for calibrating solutions
When I make test solutions (such as residual thiosulfate testing solution), standard pH buffers, 3M KCl solution for pH electrode filling, etc., I use deionized water.
for emusion making
For precipitation stage and growth stage, I use nothing but deionized water. For desalting and later stages, I use double-filtered tap water as described above.
