by Jeff Blyth
- 6g Metol (4-methylaminophenol sulfate)
- 1 litre deionized water
Dissolve up first then add:- 40g. Ascorbic acid (vitamin "C")
- 100g sodium carbonate anhydrous
- 30g sodium hydroxide
- 1 litre deionized water.
(This one should be labeled "very caustic" use rubber gloves and eye protection --guard against splashing at all.)
Just use equal volumes of A and B with the "floating dish" method. (2 close-fitting plastic dishes are arranged so that one floats ontop of the other which contains the developer. The volume in the lower dish should be just enough to give a minimal air gap so that the uptake of oxygen is minimised and the top dish can be used as a rocker to agitate developer over a plate.
Development time:- This developer is intended to react fast (to keep the silver grains spheroidal rather than filamentary, and to minimize damage to the gelatin in the strongly alkaline solution). So sufficient exposure level to give a development time of only 15-30 seconds should be aimed for .
Developer's lifetime with the floating dish method can be days, depending on usage. A yellow or mild brown color means the developer is still good. When the developer is very dark brown or black it should be discarded.
How this developer is thought to operate
The ascorbate ion with lots of alkalinity around (Na hydroxide /carbonate) is a powerful reducing agent that gets oxidized by light-damaged AgBr grains to "dehydro-ascorbate " and black or brown Ag metal grains are produced.But ascorbate ions with their negative charge are slowed from approaching the Ag+ ions in the lattice of the grain because each Ag+ is surrounded by a barrier of about 6 oppositely charged Br- ions. in the latticework, which is most often in the cubic form. (AgBr crystals can be structurally like the familiar cubic NaCl crystal , each Na+ being surrounded by 6 Cl- ions and each Cl- ion is surrounded by 6 Na+ ions ).The negative Br- ions in the lattice repel the easy access of the negative ascorbate- ions.. However “metol” is a reducing agent which is a sulfate salt and is therefore positively charged. These positive reducing ions can pass rapidly through the negative Br- lattice barricade and start reducing the Ag+ to uncharged silver metal and causing the Br- lattice ions to go into solution. But the ascorbate ions are slightly more powerful reducing agents than the metol ions so that causes newly oxidized metol ions to get returned to their original reduced form by the ascorbate ions. Therefore the metol acts as a catalyst for the ascorbate developer because it may be only momentarily oxidized.. Only when much of the ascorbate has got oxidized, do the metol ions really start to stay oxidized and oxidised metol is nearly black whereas oxidized ascorbate is merely yellow-brown. This has the useful bonus of causing the developer to get increasingly dark and this therefore acts as an indicator that it is becoming exhausted . When the developer is virtually black and opaque it means that most of the ascorbate has been oxidized and the solution should be discarded. ( Slight darkenening means the developer is OK still) . --- Another bonus about metol seems to be that it has an instant slight hardening action on soft gelatin as can be found from doing a fingernail scratch test on the notoriously soft Slavich PFG-03 emulsion after say 15 seconds immersion in “TJ1” developer made up with and without metol.