Page 66 - The Wellington photographic handbook

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It is well to remember in this connection that when hypo is
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dissolved in water a great fall takes place in the temperature of
the solution ; indeed in winter crystals of ice may sometimes be
seen to form on the outside of the containing vessel. If therefore
hypo has to be prepared for immediate use, warm water should
be employed, the dissolution of the hypo being sufficient to cool
the solution. A better plan is to prepare the hypo well in advance.
Any quantity may be so prepared, as the solution keeps indefinitely.
The strength of the hypo solution should never exceed that
given on page 48. A strong solution is less efficient than one of
proper strength, and blistering is liable to follow its use.
During washing a stream of water should on no account be
allowed to fall violently on the prints, otherwise the film may be
bruised and blisters will result. A gently flowing stream is equally
effective and much safer.
In hot climates, and even in temperate climates where the'
water supply is exceptionally soft, the use of a hardening bath
may be found necessary. The following is a satisfactory formula :
HARDENING BATH.
Alum ... ... ... ... 1 ounce 25 grammes
Water to ... 20 ounces 500 c.c.
The prints should be well rinsed after fixing, and then placed
in the above solution for ten minutes, after which they should
again be washed.
Most workers will prefer a combined fixing and hardening
bath, and provided this is properly prepared and not used for an
undue number of prints there is no objection to its employment,
The formula which follows is recommended :

COMBINED FIXING AND HARDENING BATH.
Hypo ... ... ... ... 4 ounces 200 grammes
Potassium Metabisulphite ... 60 grains 6-5
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Chrome Alum 240 25
Water to ... ... ... 20 ounces 1 litre
The hypo and metabisulphite should be dissolved in one half of the
water and the alum in the other. The two solutions should then be mixed.
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