Can I use glass enamel paint on the inside of a glass block? I am trying to avoid brush strokes.
Did you really mean you plan to paint on the "inside" of a glass block? Or did you mean the outside? I do not think I have seen anyone paint on the inside but maybe you have found a way.
There are lots of sites that give instructions for painting on the outside of blocks but most of them recommend "roughing" up the glass first if you want a truly lasting paint job. I believe most people are using either spray paint (and doing this correctly takes practice) or they are working with some sort of sponge. Streaks don't usually show up until a light is placed in or behind the block.
Just in case you are wanting something inside the block then you will probably have to drill a larger than normal hole in the side of the block. Here is a link that has some good instructions for inside and out side of blocks.
Here is a link to a free e-book that has a lot of information on this subject. It is a PDF file and is safe to use.
Glass paint does come in a spray to avoid brush strokes.
Pour a lot of liquid paint inside the glass and then turn it in many directions to coat the inside then drain the excess out the hole. Leave it upside down on a rack to drain and dry for several days.
My paint seems to run down the sides before drying, even though I'm draining the excess paint.