FIXING.
Sodium Hypo-Sulphite (or Hypo as commercially termed) may be obtained for use in either a granulated or crystal form. Its purpose is to reduce the silver salts which have not been acted upon by light. The importance of this chemical is evident, but it is probable that no part or process of photography is more abused than that of correctly preparing a fixing bath and properly fixing prints. To secure permanency prints must be fixed in a fresh solution of Hypo. When Hypo is first dissolved in water, the temperature of the solution is materially reduced. It is impor tant that the temperature of a fixing bath should be maintained as near to 5o degrees Fahr. as possible. Probably more prints fade from insufficient fixing than lack of washing, so these points should be given attention. Have plenty of solution strong enough to thoroughly fix prints in at least fifteen minutes. Always use the acid hardener in the bath as it will over come the tendency of the fixing bath to cause blisters and stains.
Our formula for preparing the Acid Hypo fixing bath is as follows : Water, 64 ozs.
Hyposulphite of Soda (crystal or granulated), - 16 ozs.
When thoroughly dissolved, add the following hardening solution, dissolving the chemicals separately and in the order named : Water, ------ - - 5 ozs.
Sulphite of Soda (desiccated), - - - - oz.
Acetic Acid No. S (containing 25 per cent. pure acid), 3 ozs.
Powdered Alum,- - - - - - r oz.
This solution will keep, and one pint of it will fix at least one-half gross of 4 x 5 prints. If sulphite and carbonate of soda in crystal form are substituted for desiccated, double the quantities mentioned should be used, The most accurate way of preparing a fixing bath is by using a hydrometer (silver actinometer), testing the specific gravity ; 70 being the correct degree.
Amateurs will find it is advisable to use our prepared solutions and the concentrated Velox Liquid Hardener is especially recommended.
Water, - - - - - - - i6 ozs.
Hyposulphite of Soda, - - - - - 4 ozs.
Velox Liquid Hardener, r oz.
NOTE—Royal Velox, unlike the other grades, should be fixed in a plain fixing bath.
Hypo, 3 ozs.
Water, - - ---- - - - 16 ozs.