Making varnish opaque?

[gp_bass]

I'm touching up the finish on an old '39 Kay, which has more of an opaque brown finish. What is usually added to varnish to make it more opaque?

(In the case of this Kay, I'm pretty sure the finish is lacquer, but I'm thinking violin varnish will be easier to work with - plus I already have some pigmented varnish mixed up.)

[ctregan]

Ground pigments will make a varnish more opaque.

These touch up powders work great, but it requires some skill.
http://www.mohawk-finishing.com/cata...asp?ictNbr=130