Much or little Metol?greenspun.com : LUSENET : B&W Photo - Film & Processing : One Thread
I've seen many recipes for developers. Some contains 2-4 grams of Metol and others use 7-10 grams. Same with Glycin. I like Agfa 8 that contains 2 grams Glycin, but some recipes use 10 grams or more. What's the point of using more of the developing agents? Is it that the developer can be used longer, or does it affect the results?
-- Patric (firstname.lastname@example.org), May 31, 2001
The composition of the developer typically is based on the intentions of the designer i.e., what kind of trade-off one is trying to make. Compare, for example, two metol based developers - D23 and FX1. The developers are designed for quite different effects and the tradeoffs required are different. D23 is designed as a fine grain developer and uses sulfite as a silver solvent - the solvency is key to achieving the fine grain. For sulphite to act as a silver solvent, it needs to be present in fairly large amounts (I believe you need at least 50gms/litre to start noting solvency effects). D23 contins 100 gms of sulphite. Solvency is also affected by the length of time the film stays in contact with the solvent. Therefore, to balance the formula i.e., have the film in for some optimum window of time, one needs to adjust either the amount of developing agent or the alkali. D23 uses sulfite itself as the alkali (and the virtue of D23 is its simlicity and preservation - in fact, Henn formulated D23 as a simpler, more reliable alternative to D76). In other words, other characteristics desired in the developer dictate the decision of no other alkali. This leads to the requirement of a fairly high amount (7.5 gms) of the developing agent, metol.
In comparison, FX1 is also a metol based developer but was explicitly formulated to provide the maximum adjacency effects possible. The mechanism that is utilized for this is the controlled exhaustion of the developing agent. This is achieved by having a small amount of the developing agent, a small amount of sulfite and using an alkali to accelerate the rate of development. It is worth pointing out here that different formulae use different methods to achieve adjacency effects. For example, HDD uses larger amounts of the developing agent (2gms/L) while reducing sulphite (1gm/L) to provide controlled exhaustion by reducing sulphites protective action, while FX1 uses lower amount of developing agent and a slightly higher amount of sulphite to provide the controlled decomposition.
In sum, it is the interactions of various components of the developer that provide the characteristics of that developer. So, things are more complicated than it appears at first sight - there does not seem to be an easy way to arrive at optimum levels for all criteria. However, the flip side of the coin is the increased flexibility one has in formulating developers.
-- N Dhananjay (email@example.com), June 01, 2001.
Very nice description DJ!
-- Pete Caluori (firstname.lastname@example.org), June 01, 2001.
Thanks for the great explanation!
-- Patric (email@example.com), June 02, 2001.