Sandarac lacquer for collodion plates

Description

The finishing coat of an ambrotype: a resin lacquer applied to a warm plate. Without it the collodion layer stays soft and rubs off at a touch.

Why it is needed

A finished collodion layer is fragile — a fingernail will mark it. Sandarac lacquer forms a hard clear film that protects the image mechanically and from damp, while deepening the shadows and giving the plate its characteristic warm cast.

How to apply it

Warm the plate, pour the lacquer as you poured the collodion — a pool tilted out to the edges — and dry it over gentle heat. A cold plate gives runs and matte patches, so temperature matters as much as an even pour.

Questions and answers

Could an acrylic spray varnish do instead?

It will protect the plate, but the look differs: sandarac gives the warm tone and depth it has been used for over a century and a half.