Wetting agent
From Silvergrain Labs
Wetting aid is used as the last step of processing to ensure even drying and reduce the risk of drying mark. Wetting aid bath is a very dilute solution of a surfactant in water. Commercial products include Kodak PhotoFlo 200, PhotoFlo 600 and PhotoFlo 2000, Ilford Ilfotol, Agfa Agepon, Tetenal Mirasol 2000 and Fuji Drywell.
Kodak PhotoFlo is provided in different concentration, since PhotoFlo 200 (used at 1:200 dilution) is more convenient for small darkroom, while PhotoFlo 2000 (used at 1:2000 dilution) is more convenient in large processing establishments. The surfactant used in PhotoFlo products is an octylphenol thoxylate. One of the most popular surfactant product of this category is Triton X-100, manufactured by Union Carbide (now a part of Dow). Thus PhotoFlo 200 is a diluted solution of Triton X-100, but because this surfactant does not mix with water very well at low dilution ratio, propylene glycol is used as a part of the solvent system. The residue of propylene glycol does not present a problem.
Wetting agent products sold by other manufacturers for darkroom use also use the surfactant of the same kind. Tetenal Mirasol 2000 contains isothiazolinone bactericide. Tetenal claims that Mirasol 2000 increases fungus resistance.
However, this author prefers a blend of secondary alcohol ethoxylates of different molecular weights, further blended with a branched secondary alcohol ethoxylate. This type of surfactant blend is very effective in lowering surface tension, even at a very low concentration. This surfactant blend also does not form a lot of bubbles, and bubbles collapse very quickly, even if formed. Thus water drips down on the materials very quickly, without leaving bubbles on the surface, eliminating the need to squeegee. This type of wetting agent is very versatile and useful, but it does not appear to be sold as a single commercial product.
In using wetting agent of any kind, it is desirable to use distilled water to minimize the ash (e.g., mineral salts) and other solid contents in the water, to further reduce the risk of drying marks. This is particularly true where tap water is hard water.
Other Uses of Wetting Agents
PhotoFlo and similar products, as well as plain Triton X-100 can be used to wet clean SP and LP records. It also makes decent windshield washer fluid and other places where thorough wetting is helpful.
However, surfactant of this type is not very useful as a coating aid, such as coating of photographic emulsions on films, plates and paper. For these applications, rapid reduction of surface tension is more important than equilibrium surface tension, so a more rapidly acting surfactant is preferred.
