Kodak Hardener F5a

Hardener for fixer

Water 125F/52C600ml
Sodium Sulfite (anhydrous)75g
Acetic Acid 28%235ml
Boric Acid (crystals)37.5g
Potassium Alum75g
Cold water to make1000ml
Mixing Instructions: Add chemicals in specified sequence. Allow solution to cool after mixing. To make 28% acetic acid from glacial acetic acid, dilute 3 parts of glacial acetic acid with 8 parts water. Use boric acid crystals as specified, do not use powder as it is extremely hard to dissolve.<br><br>A 30% hypo fixer solution is made by dissolving 300g of Sodium Thiosulfate (Hypo) in sufficient hot water to make 1L. Allow to cool.
Dilution: Add 1 part hardener to 4 parts 30% hypo fixer solution
Usage: Fix film for 10 mins or double the clearing time.

Notes 

This hardener can be added to other commercial acid fixers, but should be tested prior to use on important work. Fixing time will be less with modern rapid fixers; however, hardener will increase fixing times listed on the bottle.
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