Potash Alum Hardeners


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.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s