Varnish

Varnish is a clear protective coating applied to wood, metal, or other surfaces to enhance appearance and provide a durable finish. It forms a hard film that seals the surface, resists moisture, and guards against scratches. Varnish differs from other finishes in its drying chemistry and film formation.

Common formulations include oil-based varnishes (alkyd resins in drying oils), polyurethane varnishes, and water-based varnishes (acrylic resins). Oil-based varnishes tend to amber with age; polyurethane varnishes offer abrasion resistance; water-based varnishes have lower odor and easier cleanup. Apply in thin coats, sanding lightly between coats; follow manufacturer-recommended drying times with appropriate temperature and humidity.

Varnish is used on furniture, cabinetry, wood floors, and musical instruments to enhance grain and protect surfaces. Outdoor and marine varnishes provide additional UV and weather resistance. Proper prep—clean, sanded surfaces, compatible primers—and correct application are essential to prevent cracking, yellowing, or peeling.

Safety and disposal: varnishes contain solvents and are flammable. Use in well-ventilated areas, away from heat. Store rags in metal containers with tight lids to reduce fire risk. Cleanup depends on formulation: mineral spirits for oil-based finishes, soap and water for water-based ones.

Varnish, in computing, also refers to Varnish Cache, an open-source web application accelerator and reverse proxy. It sits in front of a web server to cache HTTP responses, reducing load and increasing throughput for high-traffic sites. It is configured with VCL, a domain-specific language that controls caching behavior.