First part of article is here.
Measure the volume of the remaining glue and pour it back into the double boiler. You will be adding 1.5 times this volume of chalk or gypsum to make gesso. Do this gradually, gently dropping each spoonful into the liquid to avoid making any bubbles. Distribute the chalk/gypsum around the pan so that it the glue soaks into it. Once all of the chalk/gypsum is in the pot, give it 10 minutes to soak. Now take a brush and gently stir the mixture, again trying to avoid making any bubbles.
For the first layer, spread it thinly over the surface of the panel, stroking back and forth in one direction. It's not very opaque when wet. Let it dry' this takes 10-30 minutes, depending on humidity and temperature (dry days are best for gessoing panels). You'll know it's dry when it feels dry to the touch and any grayish areas have disappeared.
If the gesso is getting thick, it means that it's cooling off. Replace the water in the double boiler with new hot tapwater.
You will apply 6-8 layers of gesso. Brushstrokes in each layer should be applied at right angles to those of the previous layer. Each layer is best applied shortly after the previous layer has become dry. It's best to apply all layers in one day, so that they will bond with each other. If you get cracking, that means that you're applying the gesso before the previous layer has dried. More layers will fix this. If you get little pits in the gesso, then you're painting with gesso that has bubbles in it. Let the gesso stand for a half hour before applying any more, then rub the next layer in with your hand.
Once you've applied all the gesso, let the panel dry for at least three days. You can clean the brush, pan, and anything else that got gesso on it in warm water.
Smoothing the panel
Start by using a metal file to chamfer all of the edges of the gesso, so that they are at a beveled angle inward. This protects against cracking, should the panel strike something (I've had this happen, and it's very irritating).
To get the panel smooth, I like to use a sanding block, starting with 400 grit sandpaper and moving to finer grits at the end. This produces a beautiful, eggshell-smooth finish that is almost too beautiful to paint on.
If I'm going to be painting with oil, I like to apply a final layer of hide glue to the smoothed surface of the panel. Without that, the gesso is a bit too absorbent. For egg tempera or tempera grassa, plain gesso works great.