A blue cast, IMHO indicates too much chrome alum.

Here is my formula:

Make up 10% gelatin (weight / weight) by using 10 grams of gelatin in 90 grams of water.

Add to that up to 5 ml of 10% chrome alum or 5 ml of commercial glyoxal at 4% (40% diluted to 4% with water). Chrome alum will take up to 2 days to harden, but glyoxal is done in about 4 - 8 hours.

Add 0.5 ml of surfactant such as 10% saponin, Photo Flo 200 or just plain Ethyl Alcohol (Everclear sold in some liquor stores).

Apply this mixture at the rate of 12 ml / square foot or less (not more) to the paper by any of the common methods such as brush, dip, coating blade etc...

PE