To obtain beautiful rich brown, sepia-like tones, the print is first bleached using a ferricyanide-bromide bath then redeveloped in a sulfide bath. In this process, the silver metal in the print is first converted to silver bromide than to brown silver sulfide. The end result can give the impression of print made in the late 1800's. The thiourea toner is actually a sulfide toner in alkaline solution, thiourea (thiocarbamide) reacts to yield sulfide ions, the active ingredient in the toning bath. The advantage of this process is that the foul smelling sodium sulfide bath is avoided. Thiourea Carbonate Toner is a similar thiourea based toner.

The same bleach solutions is used with Sepia Sulfide Toner 221.

CHEMICAL SAFETY

Sodium hydroxide, as a solid or in solution, is a dangerous chemical. It is corrosive and will cause a chemical burn. Its action is insidious because the burn occurs without pain. When working with sodium hydroxide, wash your hands frequently without using soap. If you detect a soapy feeling while washing, sodium hydroxide is present. In such a case wash thoroughly with soap and water. The beads or pellets of solid sodium hydroxide are easily spilled during solution preparation. If spillage occurs outside a sink, all of the spilled solid must be cleaned up. Use a damp disposable towel or tissue. If the solid is not cleaned up, it will absorb moisture from the air and form a puddle of very caustic hydroxide that will not disappear with time. Proper technique for preparing sodium hydroxide solutions is described in the Mixing Section of these instructions. We strongly urge you to wear both safety glasses and rubber gloves when working with solid sodium hydroxide or its solutions.

Thiourea is not toxic nor corrosive but, unfortunately, it is a potential carcinogen. Use rubber gloves when mixing or handling this compound or its solutions. Wash the work area, trays, and all mixing utensils with water followed by soap and water. Should a solution containing thiourea be spilled on the skin, wash immediately with water followed by soap and water. Dispose of residual solid or spent solutions containing thiourea down a drain with copious amounts of water. Potassium Ferricyanide. In spite of the fact that this compound contains cyanide, it is not particularly toxic. The reason is that the cyanide groups are bound to the iron atom and are not free to act as a poison. The cyanide groups can be released as hydrogen cyanide gas if the potassium ferricyanide is placed in a strong acid solution, however the bleach bath in this toner does not call for the use of acid. To dispose of excess potassium ferricyanide (solid or in solution), wash the material down the drain with excess water.

MIXING THE SOLUTIONS

Solution A (The Bleach Working Solution)

Chemical	Amount	Units
Water (125°F/52°C)	750	ml
Potassium ferricynide	50	g
Potassium bromide	10	g
Sodium carbonate	20	g
Cold water to make	1000	ml

Place the warm water in the temporary container (or storage container) and add the potassium ferricyanide. Stir the solution until the solid dissolves. Next, add the potassium bromide and again stir the solution to dissolve the solid. After the potassium bromide is in solution, add the sodium carbonate. As before, stir the solution to dissolve the solid. Finally add cold water to bring the final volume of the solution up to 1000 ml. Stir the final solution to ensure it is homogeneous. It is best to store this working bleach solution in the dark. Potassium ferricyanide solutions are somewhat light sensitive. Should the stock solution turn blue (from photo-formed ferrous ions reacting with the ferricyanide to form Prussian blue) the bleach has been ruined and must be discarded.

Stock Solution B (Hydroxide for the Toning)

Chemical	Amount	Units
Sodium hydroxide	10	g
Cold water	75	ml
Cold water to make	100	ml

This solution must be prepared in a sink and in a well ventilated area. Place a dry plastic mixing bowl in a sink and place the solid sodium hydroxide in the bowl. Measure out 75 ml of cold water and carefully add the water to the container. Stir the mixture with a plastic spoon until the solid has gone into solution. Stir gently and avoid splashing the solution.

When sodium hydroxide goes into solution, considerable heat is generated. If your water was not cold enough, the solution may start to steam. If this should occur, add some ice to cool the solution. DO NOT BREATH THE VAPOR. If the solution starts to steam and you cannot cool it, leave the room and let it cool off by itself. After the solid has gone into solution, let the solution sit until it reaches room temperature. Using a plastic funnel, transfer the solid sodium hydroxide solution to its plastic storage container. The transfer should be carried out in the sink. Add sufficient cold water to make 100 ml using a portion of the water to rinse out the mixing bowl. Before any of the mixing equipment leaves the sink, rinse and wash with cold water until you are positive that no residual hydroxide remains. Be sure to wash the outside of the storage container before you remove it from the sink. Should any of this solution be spilled on your skin, wash immediately with cold water followed by soap and water.

Stock Solution C (Thiourea for the Toning Bath)

Chemical	Amount	Units
Thiourea	5	g
Cold water to make	100	ml

Place the water in the mixing bowl and add the thiourea. Stir the solution until the solid goes into solution then transfer it to the storage container. Be sure to wash all utensils after use.

MIXING THE WORKING SOLUTION
Mix just prior to use. To prepare the toning solution, mix 1 part Stock Solution B, 1 part Stock Solution C, and 16 parts of water.

Image Tone	Purple-Brown	Cold-Brown	Brown (IT-2)	Warm-Brown	Yellow-Brown
Stock Solution B	20 ml	40 ml	60 ml	80 ml	100 ml
Stock Solution C	100 ml	80 ml	60 ml	40 ml	20 ml
Cold water to make	1000 ml	1000 ml	1000 ml	1000 ml	1000 ml

The toner is stable for a working session only. Dispose of the spent solution down a drain using copious amounts of water.

USING THE TONER
Correctly exposed and fully developed prints work best with this toner. This toner is for bromide papers (Patrick Dignan).

Bleaching the Print
The print to be bleached must be thoroughly washed and wet before it is immersed in the bleach solution. If residual hypo is left on the print, the hypo combined with the ferricyanide in the bleach will cause permanent loss of the image. Pour just enough Stock Solution A at room temperture to cover a print into a plastic or glass tray. Immerse the print into the bleach solution and gently rock the tray. The black image will be converted to a light brown or straw colored image in about one minute. Wash the bleached print in running water (68°F/20°C) for 15-20 minutes. During the wash, the yellow ferricyanide color on the print will be lost. Return the bleach solution to its container for reuse.

REDEVELOPMENT
Place the working solution in a plastic tray and immerse the well-washed, bleached print in it. Work at room temperature (77°F/20°C for Warm-brown & Yellow-brown). Redevelopment of the image to a rich sepia tone will occur in about 1 minute. After redevelopment, wash the print in running water for about 30 minutes.

After Treatment
The sulfide-hydroxide toning bath will soften the emulsion of the print. Therefore, it is advisable to harden the print before it is dried. Should you wish to prepare a hardening bath, use the following formula:

Chemical	Amount	Units
Water (125°F/52°C)	500	ml
Sodium sulfite	15	g
Acetic acid (28%)	40	ml
Potassium alum	15	g
Cold water to make	1000	ml

Harden the print for about 5 minutes in this bath then wash in running water for 30 minutes.

REFERENCE
Thiourea Print Toner, Kit No. 06-0065, Photographers' Formulary (800-922-5255).
Darkroom Techiques for Landscape Photography, Eddie Ephraums, p.159.
Classic Toning Methods, Peter Hughes (Reichelt), Mastering Black-and-White Photography, p.49.

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