Plaster of paris mixed with a large excess of water will give you a very fine
white powder in paste form that will not become hard. Some of that in with
your size might give you the tooth you are seeking without any appreciable
hazards and without dissolving in the size mix. Just keep it stirred up
until the plaster reaction is complete. Around 15 minutes should be plenty
of time.
You can make dextrin from starch by heating the starch in your oven. A thin
layer on a cookie sheet will work nicely. The problem is that this gives a
brown version of dextrin. The acid form stays white. As a starting point for
experiments try 300 F. You can watch it change. The deeper the color the
greater the transformation. For the cooks among you this is exactly the
transformation in the starch that you get when making a roux. In that case
butter or oil is the heat transfer medium.
Happy printing or cooking as the case may be.
Oh yes, the books I mentioned in an earlier post are taken.
Eugene Robkin.