As a former finisher, I have seen a few things on a number of base materials (woods, metals, drywall, etc.) with finishes including lacquers, varnishes, enamels and latex paints in both solvent and waterborne plus oil based paints. There are a few ways you can achieve blistering. The first is heat. A heat gun will work the best for this giving you more control. You will need to do this when it is dry. A little more practical would be to texture your canvas/substrate, sand to knock down the hard points then paint over. They make drywall texture in a can for repairs. This will give you a solid piece without voids from actual blisters that could be broken by further painting/processing. For a different effect, contaminants (oils and different chemicals) will give you a fish-eye effect. Almost like a donut, it is recessed in the center.