Yes I do. For dark blue paintings I use Damar varnish; a nice deepening of the depth and colors. Doesn’t dry for a long time. Also polyurethane for the large oil paintings before the oil goes on the paper and after the oils are dry for protection. But these small studies only certain ones are varnished. Thanks for the question.
Most of the charcoal drawings do not have any seal aside from painting acrylics on them.