1. Finishing Finishing materials
All About Oil Based Varnish
For many amateur woodworkers or hobbyists who either cannot afford spray
equipment or do not have enough space in their shop to set up a spray booth to
safely spray finishes like lacquers, brushing on an oil based varnish is one of the
best choices for a topcoat finish. Oil based varnish does not dry very quickly,
therefore it will take longer to complete a finishing project using varnish as
opposed to lacquer, water based or other faster drying finishes. However, if you
are an amateur or home woodworker, not a pro who has to worry about meeting
a deadline, time should not be top priority, quality should. Varnish has very good
resistance against abrasion, wear, heat, solvents and water vapor. Other than its
slow drying time, which can also cause problems with dust getting trapped in the
finish before it dries, the only other disadvantage to oil based varnish is that it
tends to yellow over time. The dust problem can be taken care of by setting up a
dust free finishing area in your shop and sealing it off with heavy plastic to reduce
the amount of dust and sawdust in that area. The problem of yellowing cannot be
handled as easily. First, most oil based varnishes are amber (yellowish) in color
to begin with. This is because the oils used to make the varnish are amber.
Therefore, oil based varnishes tend to somewhat change the color of the raw or
stained wood when they are applied. It is not a considerable change, and unless
applied over a very light colored or white stain, it is satisfactory. In fact, amber
varnishes actually give darker woods like walnut and mahogany a warmer
appearance. Non-amber or what are called water white finishes like some
lacquers and water based finishes can leave a cold look on darker colored
woods. However, if needed, there are a few water white varnishes available. One
is called water white restoration varnish manufactured by H. Behlen & Bro.
Nothing can really be done about yellowing of varnish over time and if you think
about it, all film finishes break down in one way or another over time and have to
be removed and replaced with a new finish. Tung oil yellows less over time than
other oils, therefore a varnish that contains tung oil will have a tendency to yellow
less over time.
Oil based varnish is manufactured by cooking certain oils that can cure with
resins. Once this blend of cooked oil and resin is complete, solvents are added to
make it thin enough to apply and metallic dryers are added to help speed up the
curing time. Initially, linseed and tung oil were used by manufactures for the
curing oils and natural resins like pine and gum resins were used along with
solvents like gum turpentine and mineral spirits (to thin it out) and lead used for
the drier. These ingredients were not only used to make varnish, but also paint.
With the exception of lead, you can sometimes still find some of these
ingredients in today's oil based varnishes, but modern varnishes usually use
synthetic resins which are superior in strength and longevity and curing oils that
are less expensive to use in the manufacturing process along with a blend of
solvents and metallic dryers like cobalt and zinc that do not cause health
problems such as lead does.
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