An Improved Potassium Alum Fixing Bath Containing Boric Acid

Most hardening fixing baths containing potassium alum tend to lose their hardening properties and precipitate a sludge of aluminum sulfite long before the fixing power of the sodium thiosulfate becomes exhausted. It is customary in large-scale practice to offset this loss in hardening properties by adding acid to the bath several times during its useful life. The addition of boric acid (5 grams per liter) to a fixing bath containing potassium alum has been found to increase the hardening life about four times and to minimize the sludging tendency to such an extent that revival with acid is unnecessary during the useful life of the bath. — A detailed study has been made of the properties of fixing baths containing potassium alum, acetic acid, sodium sulfite, and boric acid, and a suitable formula is recommended for motion picture work. Except for tropical use, it is considered that the formula containing boric acid is to be preferred to most chrome alum fixing baths which require frequent revival with acid during use'in order to maintain uniform hardening properties.

Print ISSN

0097-5834

Published

1933-08

Content type

Original Research

DOI

10.5594/J02040