What is the best way to “rejuvenate” an old brush with dried paint in it?
Dried latex paint can be removed by soaking brushes in denatured alcohol and cleaning with a brush comb. You could also use a commercial brush cleaner for synthetic brushes like Sav-A-Brush powder by Red Devil. Simply mix with water and soak brushes to remove dried paint. Oil based paint can be removed by soaking brushes in a liquid brush & roller cleaner which is especially formulated for oil based paints.
