How to test paint to see if it's oil-based or acrylic (latex): Dip a Q-tip in alcohol and rub it around on an inconspicuous test area. If the paint pools and drips, it is acrylic paint. Be careful. Alcohol can also remove acrylic paint.
How to paint perfect straight, crisp lines ***Worked awesome! We have textured walls in our new house and the paint seeps under the tape. This technique worked perfectly and I have straight, crisp lines on the walls I've painted. Worth the extra work!