Boiled linseed oil is used as a solvent for ___________ resin.
Try it first: pick an option, then read the explanation.
Understanding Oil Varnishes: Resin + Oil
This question explores the composition of an oil varnish. It's important to clarify the terminology: while the question uses the word "solvent," boiled linseed oil acts as a vehicle or binder in the final film. However, in the process of making the varnish, the hot oil does act as a medium to dissolve the solid resin.
Oil Varnish: A type of varnish made by cooking a hard resin with a drying oil (like linseed oil or tung oil). This creates a durable, weather-resistant finish. The oil gives flexibility, while the resin provides hardness and gloss.
Detailed Analysis of the Resins
The key is to identify which of these resins is commonly and easily dissolved in hot linseed oil to make a varnish.
(d) Rosin
Properties: Also known as colophony, rosin is a common, brittle resin obtained from pine trees.
Compatibility: It dissolves readily in hot oils like boiled linseed oil. This combination is used to create common, inexpensive oil varnishes. Due to its ease of use and low cost, it is a very frequent choice.
(a) Amber
Properties: A very hard, fossilized resin known for creating extremely durable and high-quality varnishes.
Compatibility: Amber is very difficult to dissolve. It requires very high temperatures and often needs to be "run" (thermally decomposed) before it will combine with oil. It is not a simple solvent process.
(b) Mastic
Properties: A soft resin typically used for fine art picture varnishes.
Compatibility: Mastic is soluble in volatile solvents like turpentine or alcohol to create a spirit varnish. It is not typically cooked with oil to make a durable oil varnish for general work.
(c) Gum
Properties: "Gum" is a very broad term. True gums (like gum arabic) are water-soluble and not used in oil varnishes. Some "gum-resins" exist, but the term is too imprecise. Rosin is the specific type of resin that fits the description.
Study Tips for Varnishes
- Oil Varnish = Oil + Resin: Remember this fundamental formula. The properties of the varnish depend on the type of oil and resin used.
- Rosin is the Regular Choice: For general-purpose or cheaper oil varnishes, rosin is the go-to resin because it's easy to dissolve in oil.
- Amber is for Artisans: Think of amber as a high-end, difficult-to-use material for premium, hard varnishes.
- Vehicle vs. Solvent Role: Understand that in this process, the oil plays two roles: it first dissolves the resin (acting like a solvent) and then hardens to form the film (acting as the vehicle).