It's a lot better to prevent trouble than to wait until you encounter it and then look about for a remedy. Our demonstrators encounter the same troubles every year as soon as the weather gets hot, and these troubles are almost always with fixing baths.

The chemical nature of an acid fixing bath changes as soon as it becomes hot. It becomes a toning bath and not a fixing bath. It isn't always possible to keep a fixing bath cool, but it is easy to make up a fresh one as often as needed. The loss of even a few prints is more expensive than the use of a fresh fixing bath, for hypo is cheaper than paper and the time necessary to make afresh fixing bath more than offsets the time required to make new prints.

Always have a stock solution of hardener on hand, and a fresh fixing bath then requires only the dissolving of a pound of hypo in sixty-four ounces of water to which eight ounces of hardener is added. The hypo must be thoroughly dissolved before the hardener is added, otherwise sulphur will be released. This will fix two gross of cabinet size paper, or its equivalent, and a smaller or larger quantity can be made up to suit the size of the batch of prints to be fixed.

A fixing bath becomes a toning bath as soon as sulphur has been released, either by chemical action or by heating. Any form of acid will release sulphur from hypo and as the hardener contains both alum and acetic acid, it must also contain a sufficient quantity of sulphite of soda to counteract the action of the acids and prevent the release of sulphur.

The hardening solution must be very nicely balanced and it is important that acetic acid should not be stronger than 28%. It is also important that pure sulphite of soda be used, as sulphite that has decomposed becomes sulphate, and sulphate of soda does not prevent sulphur being released from hypo. It is readily seen then that if the acetic acid is too strong or there is too much of it, or if the sulphite of soda is partly sulphate or there is too little of it, the balance of the solution is upset and sulphur will be released as soon as the hardener is added to the hypo solution . Be sure of the strength and purity of the chemicals you use for your stock solution of hardener.

When you dissolve a pound of hypo in sixty-four ounces of water, the temperature of the solution is so materially reduced by the dissolving hypo crystals that the hardener may be added and the bath used while cool with the best results. As it is the dissolving of the hypo that drives the heat out of the water, this advantage is entirely lost if the hypo is dissolved and allowed to get warm before it is used. Mix the hypo bath at the time you want to use it and throw it away when your prints are fixed.

Artura Iris Print, From Eastman Portrait Film Negative By Barnum Studio Cincinnati, O.

Artura Iris Print, From Eastman Portrait Film Negative By Barnum Studio Cincinnati, O.

Worn out fixing baths are probably responsible for as much or more trouble than baths which merely contain sulphur. The sulphurized bath may properly fix a print and also slightly tone it, but a bath which is worn out will not properly fix a print and may also badly bleach and discolor it. The danger lies in the print going bad after it leaves your hands.

A properly made fixing bath removes the unexposed and undeveloped silver from an emulsion by first reducing it to an insoluble silver salt and this in turn is reduced to a soluble salt which is readily removed by washing. The same action takes place in fixing plates as in fixing paper, and they are only properly fixed when they remain in a bath for some time after they become clear.

If a plate fixing bath is weak, and, in the time ordinarily necessary for fixing, only the insoluble silver salt is formed, it can not be removed by washing and as soon as the negative is exposed to light a stain will appear. This stain can not be removed and can not be prevented except by proper fixing in a bath of proper strength. The mere fact that a negative will become clear with long fixing in an old bath doesn't mean that it is fixed. There must be an excess of hypo to render the silver soluble so that it can be washed out of the gelatine emulsion.

Fixing is the important thing - more important, in fact, than washing. Agitated water will remove half the hypo from a plate in two minutes. In another two minutes half the remainder is removed, and so on until washing is complete. If three-quarters of the hypo is removed in four minutes, fifteen minutes should be time for thorough washing under the proper conditions.

Double the time that it takes to clear a plate should be allowed for fixing, and if the bath is fresh the plate will be better for the long fixing and comparatively short washing, and the gelatine will not likely soften even in hot weather.

Prints should always be washed longer than plates for, while it does not take any longer to remove the hypo from the gelatine, a longer time must be allowed to thoroughly remove the hypo from the paper.

Be sure your fixing baths are fresh and of proper strength, be sure you do not overwork them and be sure that the chemicals that go into your baths are pure. Keep sulphite of soda in an airtight container and do not use acetic acid over 28% strong. You can be sure of your chemicals if you use only those bearing the C. K. Co. Tested Chemical Seal.

Artura Iris Print, From Eastman Portrait Film Negative By Barnum Studio Cincinnati, O.

Artura Iris Print, From Eastman Portrait Film Negative By Barnum Studio Cincinnati, O.