Originally Posted by dmax
First, you have "sparkles" which are grains of undisolved gelatin. To help dissolve the gelatin better always let the gelatin bloom and dissolve before heating.
Second add about 50 ml of grain alcohol for a half liter solution of gelatin. This will aid in dissolving the gelatin.
Third if you are going to gelatin size, use a about a 3% solution of gelatin.
Fourth, always weight the gelatin in the packets as there may not be the quantity of gelatin marked on the packs.
Fifth, you don't mention why you are sizing paper for these processes to begin with. Normally for VDB or cyanotype you don't need to gelatin size if you are using a "good" paper. Why do the extra work if you don't need to?