Potash Alum Hardeners

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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.

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