The Function of a __________ in varnish is to accelerate the process of drying.
🔬 Understanding How Varnish Dries
The "drying" of an oil-based varnish is a two-stage process. First, the volatile solvent evaporates, leaving the surface tacky. Second, a much slower chemical reaction called oxidation occurs, where the oil vehicle reacts with oxygen from the air to harden, or "cure," into a solid, durable film. The question asks what accelerates this second, crucial step.
Drier: A chemical compound, typically a metallic salt, added in small amounts to an oil-based varnish or paint to act as a catalyst. It dramatically speeds up the rate of oxidation, allowing the film to cure in hours rather than days.
⚖️ Detailed Analysis of the Options
Let's examine the role of each component to understand why 'Drier' is the correct answer.
(d) Drier
Function: To accelerate the chemical curing (oxidation) of the oil vehicle. It is the only component whose specific job is to make the varnish harden faster. Common driers are metallic salts of lead, cobalt, or manganese.
Role: Catalyst.
(a) Solvent
Function: To dissolve the resin and oil, making the varnish thin enough to apply. The evaporation of the solvent is the first stage of drying, but the solvent itself does not accelerate the chemical hardening of the oil. In fact, a slow-evaporating solvent can increase the overall time it takes for the varnish to feel dry.
Role: Thinner / Evaporating liquid.
(b) Resin
Function: The resin is the primary film-forming solid. It provides hardness, gloss, and durability to the final finish. It is a core part of the film itself, not an accelerator.
Role: Film-former / Solid component.
(c) Coolant
Function: A coolant is a substance used to reduce or regulate temperature in systems like engines or machinery. It has no function in paints or varnishes.
Role: Unrelated to coatings.
💡 Study Tips for Varnish Components
- Drier makes it Dry Faster: The name is a direct clue to its function. Driers are drying accelerators.
- Distinguish Physical vs. Chemical Drying: Solvent evaporation is physical drying (liquid to gas). Oil hardening is chemical drying (oxidation). Driers affect the chemical part.
- Resin is the Backbone: The resin provides the strength and gloss of the final product.
- Solvent is the Helper that Leaves: The solvent makes application possible and then evaporates away.