This is a pretty good tip.
When I used to own a bandsaw and there is a mixed emotions on its sale, I used to push the blade with my finger and test the tension that way. But the above article in my view is a much better alternative.
Wood has long been protected and finished with oil; oil finishes date back at least two millennia. Both Linseed and Tung oil does enhance the beauty of the wood. However, there are certain distinct differences between the two that I will go into another article on the subject. To improve o penetration, solvents like turpentine, mineral spirits or citrus solvents are added; driers are applied to speed up the oil’s drying; resins and waxes are added to provide surface protection. There is nothing quite like the feel of a piece of wood that has been coated with oil. With an oil finish, the wood itself can be felt rather than a covering.
HOW THEY WORK
Not all oils are suitable for finishing wood, such as mineral oil won’t dry at all.
Shellacs and lacquers do not undergo chemical reactions; instead, they simply lose their solvent and the material is left behind as a distinct film. By immediately applying the same solvent again to the film, it can be dissolved once more. Linseed oil, tung oil, and the other drying oils cannot be redissolved in any way with their original solvent.
Tung oil has been used for many centuries.
Tung oil served as the foundational component for the traditional oriental lacquer finishes. The pure tung oil is thicker than you may anticipate when you pour it out of the can. For better penetration, particularly during the initial layer, most people thin it with mineral spirits, turpentine or the natural route Citrus solvent. Tung oil is more heat- and water-resistant than linseed oil.
POLYMERISED TUNG OIL
According to some, polymerised tung oil is superior to pure tung oil. To polymerise tung oil, it is heated to roughly 360 degrees and bubbled with oxygen. The end result is polymerised tung oil, a comparable but brand-new substance that dries quicker and has more lustre than pure tung oil. Polymerised tung oil can be used “straight” or combined with different varnishes, much like pure tung oil.
The very slow drying time of varnish makes it easy for a wet layer to gather dust, and it’s challenging to apply without leaving brush marks. Therefore, oil or an oil/varnish combination is recommended for the majority of projects by YouTubers and magazines in particular. Dust is not a problem because oils are easy to apply with a rag, and they penetrate.
The oils and oil/varnish combinations provide a dull, satin finish that is perfect for modern, casual designs. However, oils lack the depth, surface protection, and formal appearance of a varnish finish.
A completely smooth, high-gloss finish on a piece of furniture in the 18th and 19th centuries was a symbol of superior craftsmanship; only the wealthy could afford it. A wide range of mysterious natural resins and gums were stored in the cabinetmaker’s workshop; they were derived from insects, plants, and unusual objects that had been dug up from the ground.
To create a spirit varnish, these natural resins were pulverised and then dissolved in an alcohol solvent made from brandy and wine. Or they were added to a natural oil to create a varnish known as fixed-oil. Each shop has its own special formulas for getting the “ideal” finish.
Although these vintage finishes were lovely, they had a limited shelf life and were challenging to use. They also wouldn’t withstand the abuse that is anticipated of today’s finishes. Varnishes today are different. They are created using countless mixtures of synthetic (man-made) resins, oils, pigments, and solvents. Unfortunately, no two varnishes can be combined to create one that is ideal for all projects.
SOLIDS AND SOLVENTS
A non-volatile part (the solids) and a volatile part are the two fundamental components of all varnishes (a liquid solvent such as mineral spirits). The real material (resins and oils) that is left behind after the solvent evaporates is referred to as the solids. The sole function of the solvent is to transport the solids to the surface. Since it evaporates, it doesn’t provide any surface protection.
The resin is the most significant component of the solids. Alkyd, phenolic, or polyurethane are three durable synthetic (man made) resins that are used to make the majority of varnishes today.
Any varnish that is marketed as an ordinary “oil base varnish” was most likely produced using an alkyd resin. This synthetic resin is created chemically when an acid and an alcohol are combined. Alkyd varnishes are relatively flexible and resilient, although they can only withstand moisture if tung oil has been added (typically, linseed or soya alkyd is considerably more frequent). The least expensive synthetic varnishes are alkyd varnishes, which are ideal for projects that will be kept inside and won’t be subjected to a lot of harm.
Because oil is less expensive than resin, producers frequently use a cheaper oil to generate a product with a higher oil to resin ratio. The qualities will also change depending on the type of oil added to the resin. The most durable and moisture-resistant oil is tung, but it is also the priciest. Some producers will use a very tiny amount of tung oil for toughness and moisture resistance before using linseed or soya oil because tung oil is 40–45% more expensive than linseed or soya oil.
Though these other oils do have certain benefits, this may not be entirely a bad thing. Soya oil yellows even less than linseed oil, which yellows less than tung oil. Linseed oil can also soften resin if it’s too hard.
GLOSS VS. SATIN
By using a pigment, usually silica, varnishes can be further altered. The goal is to achieve a satin shine by diffusing the light that is bouncing off the surface.
Four issues exist with satin varnishes. To ensure that the pigments are evenly distributed throughout the varnish, they must first be swirled. However, swirling any varnish can result in air bubbles that interfere with the application of the varnish.
Second, some resin must be excluded when silica is added. A satin varnish won’t hold up as well because of this. Third, silica is merely a contaminant and very fine sand. Particularly after several coats, it obscures the wood’s grain and clouds the surface.
Finally, the gloss of a coat of satin varnish depends on the thickness of the coat. Additionally, the thickness of the film typically changes from the start to the end of a brush stroke. But until it dries, these discrepancies cannot be observed.
If you desire a matte finish, you can choose between two options. First, merely apply a final coat of satin varnish. After applying a few layers of gloss varnish, sanding it thoroughly, a consistent satin top coat should be applied.
Utilising a gloss varnish for each application is another option. Once it has dried, rub it with steel wool to remove any remaining sheen.
So which varnish is ideal for a project?
The varnish must be flexible, contain phenolic resin, tung oil, and ultraviolet absorbers if it is to be used on a project that will be exposed to the elements.
A polyurethane resin or phenolic resin, as well as maybe tung oil, should be used in interior durable applications.
Finally, don’t be hesitant to try new things. Experimentation leads to knowledge, and knowledge leads to success.
Every book finishing article I’ve ever read emphasises the value of using a good brush. The author usually refers to a natural bristle brush when he says “high quality.” Finishers debate the relative merits of various natural bristles, such as Chinese hog, civet cat, and even camel hair, which is actually derived from the tail of Russian squirrels rather than a camel. While I do have high-quality brushes, there is one more that is underutilised but excellent for varnish.
The benefits of an inexpensive polyfoam brush for varnish application: No brush strokes, little to no air bubbles, and a uniform, smooth coat are the benefits. They are entirely disposable and reasonably priced.
There are only two issues I can identify with polyfoam brushes: They aren’t the best for spindles or mouldings, to start. Too much varnish is absorbed by a polyfoam brush, which leaves heavy deposits in crevices.
Additionally, as the solvents in lacquer and shellac may disintegrate the foam, polyfoam brushes should not be used with these products. You should not use them with any finish that employs lacquer thinner as a solvent, even though they work fine with varnishes.
Here’s the goal: finish a table-top to a rich, lustrous, hand-rubbed, satin sheen – the kind of finish you want to touch with your fingertips just to make sure it’s real. It can be done in a home shop, but it takes a lot of work, and even more patience.
The first step in producing that kind of finish is to get the table-top as smooth as possible. Plane the top flat and smooth.
APPLYING THE FINISH
The table-top is smooth and ready for the finish.
The basic procedure is to apply stain (if you want to), then several coats of sealer, and finally the varnish.
If the top is made up of boards of slightly different colours, you’ll probably want to apply a stain to even things out.
Before proceeding any farther, sweep the shop clean of all sawdust. Then wait a day for the dust to settle before applying the sealer. Set up a finishing area with good ventilation, but free of drafts.
THE SEALER COATS
Both of the tables we finished are walnut. It’s usually recommended that you apply a paste filler to open grained woods like walnut. To be honest, I’m not particularly fond of working with paste fillers. They’re a mess. Besides, three coats of sanding sealer does the job nicely.
Most sanding sealers are formulated for use with lacquer finishes.
To apply the sanding sealer, I used one of those newfangled foam poly brushes, brushing it on as with any other finish.
As you apply the sanding sealer, watch for drips and runs. If there’s a run, dip the brush in some mineral spirits and brush it out.
It will take several hours for the sealer to dry, depending on how thick the coat is, the temperature, and the humidity. When it is dry, use 400-grit silicon carbide paper to sand out the roughness. As you start to sand, you should get a very fine white powder. If, instead, the sealer gums up on the paper, it means it’s not dry yet.
Apply another coat of sealer. After this coat is dry, hold the table-top at an angle under a fluorescent light. Look closely at the surface. If you see little pockets (pores), it means the grain isn’t filled yet, and one more coat is needed.
VARNISH TOP COAT
When all the grain pores are filled, you can apply the varnish. Before you start, make sure the surface is clean of all dust – go over it thoroughly with a tack rag. The biggest problem with varnish is that it takes so long to dry. In order to dry properly, you require a good environment: room temperature between 70° and 80°, low humidity, good ventilation but no drafts.
During the drying time, the varnish is very susceptible to dust from the air. So, the finishing area must be dust-free. It’s best to protect the table-top with a piece of plywood right after you’ve applied the varnish.
Besides dust, the biggest enemy you have to face is bubbles. Do not shake the can of varnish, stir it gently. Load the brush with varnish (fairly full, but not dripping) and spread it across the grain. Continue until the entire top is covered. Then tip off’ any brush marks by pulling the brush with the grain.
This coat of varnish will take forever to dry. Allow at least a day, maybe more. Test it by pressing your thumb on the surface. If a thumbprint appears in the finish, it’s not dry.
Before applying the second coat, the surface must be sanded smooth. Again, use 400-grit silicon carbide paper. Be very careful not to sand through the varnish, just take out the bumps.
After the final coat of varnish is dry, the surface will probably look quite glossy, but uneven with some bumps of dust particles. What you want, of course, is a smooth, hand-rubbed satin sheen.
To get a hand rubbed finish you need three things: pumice stone, rubbing oil and a felt pad. Pumice stone is a very fine abrasive powder. It used to be available in a range of grits, but now is usually sold in one grit only: “FF” the medium grit.
Rubbing oil is a light oil that suspends the pumice stone, so it can be worked over the surface of the finish.
Soak the felt pad with some rubbing oil. Pour a little pumice stone in a small pan and dip the felt pad into it, or pour a little oil on the surface and sprinkle the pumice stone on top. Then start rubbing.
Rub with the grain in long, even strokes. Don’t try to overdo it, just rub with medium press until you feel the pumice stone start to cut. The more you rub, the shinier the finish becomes. (You don’t want to rub too much, or you’ll go through the varnish.)
Every once in a while, clean off the oil and pumice with a soft cloth to see what you’ve got. You can stop whenever you get the sheen you want. If you want more of a shine, switch to rottenstone and go through the same process.
When you’re done, wipe off all the oil and abrasive powder. There will be a thin layer of oil left on the surface; it will dry out in a day or so. You can buff the top with a Jamb’s wool pad and leave it that way, or apply a paste wax. Finally, run your fingertips across the top, just to make sure it’s real.