Varnish was once made by cooking oils, such as linseed and soya (modified soybean) oil, with a resin. Today, these natural resins have been replaced by synthetic resins, such as polyurethane and alkyd. Varnish finishes range from flat to gloss, with a satin finish probably being the most popular.
"Spar" varnish means there is a higher ratio of oil to resin, making it softer and more flexible. This makes it better suited for outdoor projects. By contrast, indoor varnish is harder because it has a higher
Polyurethane varnish (oil-based) darkens and adds an amber tone to the wood, but not as much as linseed oil.
Water based finishes add no color, but they do darken the wood.
Boiled linseed oil darkens and adds an amber tone to the wood.
^ Orange shellac adds a warm orange color.
Lacquer adds very little color.
ratio of resin to oil. When applied in multiple coats, varnish produces a very durable, protective finish.
Varnish can be thinned with mineral spirits or paint thinner to make it easier to wipe on wood. In this case, it is called "wiping varnish" and is widely marketed this way. Wiping varnish requires more coats than un-thinned varnish to achieve the same film thickness.
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