Paper prep is important for most historic processes. An additional sizing step before the light sensitive processes can really improve the print quality, and remedy problems. Gelatin is a commonly used sizing agent with a hardening agent like chrome alum or formaldehyde that polymerizes the gelatin, rendering it insoluble. I’ve experimented with plain alum (Potassium Aluminum Sulfate) from grocery stores as a hardener with success, even with carbon printing. Pictured is two different sizing techniques that I’m currently testing.
Left: Floated on a hot bath of 5% gelatin, 1.5% alum, 15% vinegar.
Right: Two bath sizing. Submerged in 5% gelatin . Hung to dry. Then submerged in 3% alum bath for 15 minutes.
The two bath sizing has a less textured, less glossy, and clearer sizing. The one bath sizing has a thicker coating, and a yellowish discoloration. Perhaps just more noticeable because the thickness of the coating, perhaps the vinegar reacts to the gel/alum. The vinegar addition is necessary as the gel/alum bath immediately thickens to the point of being inoperable. Vinegar will remedy this, even after the effect takes place.
Andrew Musil 