A tack rag is made from a cotton or cheese cloth rag that has been soaked with a thinned varnish. It is used to help pick up small dust particles before you begin applying varnish, stain, sealant, or polish. If you don't use a tack rag it is possible that the dust particles will be sealed underneath the surface and causes the polishes to become dim or not as glossy.
Step 1 - Dip Rag
Dip a rag made from cotton or cheese cloth into water and squeeze it dry.
Step 2 - Add Turpentine
Sprinkle a little bit of turpentine onto the rag, but not too much.
Step 3 - Add Varnish
Sprinkle on three tablespoons varnish over the surface of the rag and work the material to mix them together.
Step 4 - Wipe Surface
Wipe the tack rag over the surface of your project and let dry before you begin to apply the sealant.
Disposing of a Tack Rag
As with any material that has a varnish or turpentine on it, you must take special precautions while disposing it. Storing varnish and turpentine requires thoughtful care, since they're both capable of spontaneous combustion when they are left on a crumpled rag or in the sunlight. Rinse the tack rag with water and lay the rag flat on the ground or a table while it dries.