What is a true statement regarding copal varnish?

The statement that copal varnish helps prevent tooth discoloration from amalgam is accurate because copal varnish acts as a barrier between the tooth structure and the amalgam restoration. When amalgam comes into contact with dental tissues, it can create a discoloring reaction, particularly in areas of the dentin. The application of copal varnish seals the tooth surface and reduces the potential for this discoloration, showcasing its protective role in dental restorations.

The other options do not accurately describe the properties or functions of copal varnish. While viscosity and color may vary, there is no requirement for it to be dark yellow and viscous. Additionally, copal varnish typically evaporates quickly to allow for subsequent procedures to be done without delay. Finally, using one coat is generally not considered sufficient; multiple coats may be applied to ensure effective sealing and protection.