This past week I did a final scraping and sanding, and applied the sealer. I used the usual egg white. The first coat was applied with a rag, the second with a brush. The egg white caused the red paint to run, so I decided to turn accident into a feature, and spread the red over the button. As we say in the software business, "It's not a bug, it's a feature!" The instrument is now hanging to thoroughly dry.
I will be in Europe on business this coming week, so my next opportunity to work on the violin is probably mid-April. That should work out fine, as I need pleasant weather for the multiple varnish coats to properly dry.