Baths for A4 sheets using A4 trays.
We use very low-cost plastic “Kitty Litter” trays. The coating procedure should be kept quite separate from the later photosensitizing procedure which is done just before the exposure and development procedure. So one can use the same trays after carefully washing them free of the chemicals used in the initial coating procedure. We use 2 trays to hold 2 solutions for initially coating sheets, and then we dry the sheets well. Later we need 1 tray to make the sheet photosensitive and one tray to hold developer after the exposure and 1 tray to hold a final treatment after development. This last tray ideally needs an extra tray to act as a floating lid on about 1 litre of liquid to minimise oxygen absorption. A minimum of about 250ml of liquid is needed for a bath so that it completely covers the smooth floor of an A4 tray. For A3 sized sheets we use polypropylene storage trays.
Thionine dye bath.
For the Epson “Semigloss” photopaper, we add 1.0g thionine acetate (or chloride) to a clean 1 litre beaker , then we add 260 ml of hot (~70 oC) de-ionized or distilled water (DI) This is then stirred for about 15 minutes. For the Jessops Satin photopaper we start with 1.3g of thionine dye and then we add 260 ml of hot (~70 oC) de-ionized or distilled water (DI) This is then stirred for about 15 minutes. The thionin solution is then left to cool for several hours before use. During this time, thionin forms peculiar aggregations of molecules such as dimers and trimers [ 1 ] so that one can later get richer dye coatings from cold solutions than hot ones. Once in a tray the cold solution can be used indefinitely but needs to be stored in a bottle to stop water evaporation. We have recently been surprised to find that coating works best without the addition of alcohol, or a surfactant. (In contrast to our previous recipe).
Potassium ferricyanide bath.
About 150g of potassium ferricyanide is stirred into 1 litre of DI in a jug or beaker until dissolved. In a tray, it can be used indefinitely, but should be stored in a bottle to prevent too much water evaporating.
The Photosensitizing bath. Either using DEA or the TRIS BASE alternative.
100.0g (not ml.) diethanolamine (DEA), is stirred into 200 ml. of DI and stirred to form a clear solution (soln.) in a glass or plastic beaker or jug. Then 91g of EDTA powder (N.B. NOT the sodium salt form of EDTA) is poured in and stirred continuously until a completely clear solution results. The clear solution may warm up to about 35o C during this neutralization step. This quantity of liquid is sufficient to cover the floor of one of our A4 trays. (The pH finishes up at around 7 when it has cooled down to about 20 oC.). This concentrated solution keeps well and can be used many times, it just needs protection from evaporation in the long term.
If TRIS Base is being used instead of DEA, The same method is used as for DEA but the ratios differ to get to a neutral pH. 20g TRIS Base is stirred into 200ml of warm DI (~50 oC.) and then 100g EDTA (Not the sodium salt) is stirred in for as long as it takes to get a clear solution. (The pH finishes up at around 7 when it has cooled down to about 20 oC.).
Ferrous sulphate bath or developer bath
We stir in 20g. sodium bisulphate to a litre of water in a beaker or jug (tap-water is quite OK here, cold or warm from the hot tap is better than using cold water from the cold tap as it will contain less oxygen). Then about 15g. of ferrous sulphate is stirred in. This is then poured into a tray. This acidic solution slowly absorbs oxygen. It works well to use another tray as a floating lid when the solution is not in use, it can then last for days.
Sulphite bath. (The final bath).
About 30g. anhydrous sodium sulphite (Na2SO3) is stirred into 1 litre tap water in a beaker or jug. This somewhat alkaline solution will absorb oxygen more rapidly than the previous solution. when it is in an open tray. It works well to use another tray as a floating lid when the solution is not in use.
Blyth, J. & Richardson, M. De Montfort University, The Gateway, Leicester, LE1 9BH
Non-holographic imaging systems