[Timothy C. Tyler]

I would be surprised if JSS used Permalba White as we know it. Here's detail of his work. Permalba slips off a painting's surface like motor oil.

This is the point I make to students; if you start with a lean, "thick" white you can add your trusty medium of choice and make any white oily.

If you start oily, you have to set it out overnight on cardboard or such surface to let that suck the oil from it.