I was looking for some advice on sizing ceramic tiles for cyanotypes and came across Photo Engineer´s APUG recipe: 10 g 250 BI photo grade gelatin 90 g Distilled Water at RT Mix and gradually raise to 40 deg C. Add 5 ml of 10% Chrome Alum solution. Add a suitable wetting agent if needed if tests show problems coating. Spread on clean, grease free tile at about 10 - 15 ml / foot square. Allow to cure for about 1 week. Has anyone tried this successfully? Is it possible to do the same using some kind of varnish instead?