How do you varnish or preserve an acrylic canvas painting that has some charcoal in it?

To varnish or preserve an acrylic canvas painting with charcoal, first ensure the painting is completely dry, which may take several days. Gently brush off any loose charcoal particles using a soft, dry brush to avoid smudging. Use a spray varnish specifically designed for acrylics, applying it in thin, even coats from a distance to avoid saturating the charcoal. Allow each coat to dry thoroughly before applying additional layers, typically no more than three coats for optimal protection.