Author Topic: finishing formula  (Read 6756 times)

hschappell

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finishing formula
« on: April 14, 2007, 04:25:45 PM »
I would like to know a formula for mixing a varnish,boiled linseed oil and either turpentine or thiner. I have seen the proportions as one-third of each, but am not sure.Also what can be expected as far as protection from moisture and durability?

Freddy Roman

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Re: finishing formula
« Reply #1 on: April 14, 2007, 04:34:22 PM »
THE SECRET FORMULA IS!!!!!!!!!
1 PART BOILED LINSEED OIL
2 PARTS VARNISH
3 PARTS TURPS

DURABILITY DEPENDS ON QUALITY OF VARNISH USED, BUT ALL AND ALL IT IS VERY DURABLE.  IN REGARDS TO MOISTURE I HAVE NOT HAD ANY ISSUES.  IT IS A GREAT FINISH USED OFTEN AT THE FURNITURE INSISTUTE OF MASS.

FREDDY ROMAN
MAKER AND RESTORER
Freddy Roman
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Alan Chase

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Re: finishing formula
« Reply #2 on: April 15, 2007, 03:02:58 PM »
I've been using this formula sucessfully for years, I tend to mix in a little more varnish, may half varnish one third oil and one third thinner. I don't really think it makes a lot of difference, the more varnish the fewer coats are needed.

HSteier

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Re: finishing formula
« Reply #3 on: April 16, 2007, 12:22:45 PM »
Linseed oil used alone as a finish causes darkening over time. Does it do the same thing when mixed with varnish?
Several manufacturers make "oil finishes" that contain a mixture of linseed or other finishing oil and varnish. How do these differ from the "magic formula"  especially since there seem to be several magic formulas?
Technically isn't an oil varnish mixture just a combination of two film finishes that "dry" by oxidation/polymerization? What benefit does this have over a quality non-yellowing polyurethane?

Thanks,

Howard Steier

dkeller_nc

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Re: finishing formula
« Reply #4 on: April 18, 2007, 02:30:12 PM »
From a technical perspective, polyurethane IS a varnish.  The definition of a varnish is a polymerizable substance mixed with an evaporative carrier (typically mineral spirits, and more rarely, turpentine), where the polymerization occurs by exposure to oxygen in the atmosphere.  All varnishes leave a film coating behind after curing (a pure oil finish, either linseed or (pure) tung oil, does not leave a film).

The historic varnishes were usually a mixture of fossilized or dried tree resins (e.g., amber and/or copals), gum resins (such as mastic or pine rosin), linseed oil, and turpentine as a thinner and carrier.  The linseed oil had a dual purpose - dissolving the resins when heated, and softening the ultimate cured finish somewhat to make it more flexible.

A modern varnish is similar - it contains a petroleum-derived resin (either alkyd or urethane) and a carrier.  In the case of alkyd varnishes, some amount of plant oils are added (such as linseed, but sometimes safflower) to make the ultimate cured finish more flexible.  In the case of polyurethane, the flexibility of the ultimate cured finish is controlled by the particular molecular formula of the urethane, with more polymerization resulting in a harder film, and less resulting in a more flexible (or softer) film.

Jeffrey Greene's book 18th Century American Furniture contains a good bit of historic information, and both Bob Flexner's book Understanding Wood Finishes and his recent article in Popular woodworking discuss the differences between varnishes, oils, and evaporative finishes.
Period Furniture & Carving as a hobby - about 20 years woodworking

HSteier

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Re: finishing formula
« Reply #5 on: April 19, 2007, 08:17:23 AM »
I appreciate the reply. I understand that polyurethane is one type of varnish. My question is "what is the advantage of adding an oil to varnish?" The oil dries by oxidation/polymerization and generally more slowly than the varnish and oil makes the dried finish less "hard" and therefore has less luster. Is it easier to apply? Does it provide a certain look that varnish doesn't provide? Why is it "a great finish" used frquently by the Furniture Institute of Massachusetts? In other words what advantage does it have over any modern varnish used out of the can?

Howard Steier

dkeller_nc

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Re: finishing formula
« Reply #6 on: April 19, 2007, 09:15:47 AM »
There are several reasons for modifying a varnish with a drying oil.  Typically, the oil will result in a more flexible finish, so wood movement won't cause the finish to crack.  It also will delay the curing and improve the flow characteristics somewhat, so it will level better when brushed or padded on.  Finally, oil will dramatically enhance the grain in figured wood.  A good test to illustrate this difference is to apply a water-based poly and an oil-based poly to different patches of the same board.  The water-based finish will look quite dull in comparison.

On the other hand, too much oil will result in a finish that is really too soft to sand, and will take a very long time to cure.  For the most part, I use urethanes straight out of the can, because a good deal of engineering of the formula has already been done to balance hardness, cure time, and flowability.  I also usually apply these by brush or pad, though, and they'd likely need to be thinned if the intent is to spray them on.

As a note, all solvent and oil-based finishes will yellow somewhat over time, although pre-catalyzed laquer finishes do so less than alkyd/oil and solvent based poly finishes.

Finally, and this is just my opinion, I haven't and wouldn't apply poly to a historic reproduction.  Even the film-based finishes in use in the 18th and 19th did not build to a very thick coat.
Period Furniture & Carving as a hobby - about 20 years woodworking

Antiquity Period Designs, Ltd.

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Re: finishing formula
« Reply #7 on: April 20, 2007, 08:18:38 AM »
I simply buy my favorite can of wipe on finish from the hardware store or wood working store.  Been doing this for 22 years and have never had a customer complain about the finish.  Why re-invent the wheel (by mixing your own)?

Dennis Bork
Antiquity Period Designs, Ltd.
Professional period furniture maker since 1985.  Received a B.S. degree in physics then apprenticed and worked as a wood patternmaker for 12 years. Retired Dec. 2018.

HSteier

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Re: finishing formula
« Reply #8 on: April 20, 2007, 10:17:30 AM »
Dennis,
Do you use wipe-on instead of brush-on for ease of application or is there some other feature that you like? What brand do you use? For traditional or polyurethane varnishes I have found that three or four coats are necessary. How many coats do you typically need for wipe-on?

Howard Steier

Jeff Saylor

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Re: finishing formula
« Reply #9 on: April 20, 2007, 11:38:37 AM »
Howard,

I've been using General Finishes Arm-r-seal oil & urethane topcoat wipe-on formula for high wear surfaces (tabletops, etc.).  Right now, I'm using it on a pair of Chippendale mirror frames that are going to go into bathrooms because of the humidity and the frequent cleaning of the mirrors.  I believe I picked up on this product from Dennis Bork on the old forum.  It seems to be pretty tough stuff- I like it.
Jeff Saylor
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awleonard

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Re: finishing formula
« Reply #10 on: April 26, 2007, 02:55:32 PM »
I've used the General Finishes stuff on several projects.  Even on a breakfast room table that gets heavy use.  Great product and very forgiving to apply. 

Tony

Antiquity Period Designs, Ltd.

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Re: finishing formula
« Reply #11 on: April 26, 2007, 03:00:50 PM »
GF now has a water base varnish.  I now use it instead of their oil finish.  Dries 2-4 hours and almost no odor.  No lap marks even on large table tops and it dries crystal clear.  Try it!

Dennis Bork
Antiquity Period Designs, Ltd.
Professional period furniture maker since 1985.  Received a B.S. degree in physics then apprenticed and worked as a wood patternmaker for 12 years. Retired Dec. 2018.