Formaldehyde hardener bath

Description

It toughens the gelatin layer so an emulsion survives high temperatures, long processing or physical contact. Needed wherever ordinary film softens and slips.

When it is unavoidable

Old film with an unhardened emulsion, processing at 38–41 °C, hand processes with long immersion, and emulsions you coated yourself. In all of these the gelatin swells and can lift from the support; a hardener bath prevents it.

Handle with care

Formaldehyde is volatile and irritates the airways. Work in a ventilated room, wear gloves, and do not warm the solution.

Questions and answers

Does modern film need it?

Usually not — modern emulsions are hardened in manufacture. It is for old materials and hand-coated emulsions.