Sealer varnishes are very important in the furniture varnishing process. Depends on the final appearance, they must get some requirements. (transparency, elasticity, easy sanding, flush, filling capacity and fast drying), if we want to get a top quality sealer.
The main function of that sealer varnishes is to fill and cover the pore or small imperfections that may have the wood, in order to get uniform and level surfaces.
In general, sealer varnishes should be formulated with agents to make easer sanding with maximum transparency if they are colorless, and with maximum elasticity to prevent breaking if they are white varnish.
They should have enough capacity to cover correctly the surfaces and be fast drying, because they are faces that must be sanded before applying the topcoat.