I'd like to how do I get acrylic paints to be permanent on slate? What finish should I put over it? It will be used outdoors. I am putting on a coat of Marine Varnish now.
Your Marine Varnish should work just fine. You could use any outdoor varnish. Some people do nothing at all over the acrylic paints and have had rocks or garden stones outside for years with no damage to the paint
Best of luck.