How to keep raw canvas edges from fraying?

masking tape or duct tape

Dritz Fray Check – sold anywhere that sewing supplies are sold.

Hairspray or hair gel.

Candle wax

hot glue

Thanks everyone. Superglue and elmer’s was all I could find around here…. seems to be working okay…

Cutting the edges with pinking shears may also help.

It depends on what you are doing with it. You can dilute elmers glue and paint the edge both sides soaking the edge. it’s way cheaper than using Dritz or nail polish and easier than using wax.
When I am painting a floor cloth I use this method to seal the edges which I fold under after applying gesso to the canvas. I hot glue under the hem. There has been occasion when I didn’t want to have a hem and the edges soaked in diluted elmers hold up perfectly well on their own.