A general rule is that it is always best to varnish an acrylic painting if the possibility exists. It is applied when the painting is finished and dry. First and foremost, it is to protect the paint from scratches, dust, dirt, etc., but also the pigments in the paint so that it is not damaged by ultraviolet light. There are both glossy and matt varnish and you can mix Liquitex different types to get the exact faintness or shine you want.
This is the glossy one that is semi-transparent when wet, transparent when dry. Increases gloss, depth and color to the site in the color it is applied over. For hard surfaces and is not removable. 118ml.