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Sanded-in Oil Finish

Discussion in 'Luthier's Corner' started by Jazzdogg, Nov 30, 2007.

  1. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA
    I received an inquiry via PM from a fellow TBer who is interested in obtaining a copy of a tutorial I wrote several years ago for furniture and cabinetmaking students at a local college.

    Unfortunately, I found that I was unable to attach a document to a PM, so I am pasting the tutorial below, in the off chance that a few other TBers might also be interested.

    There's a lot of tangential information at the beginning of the tutorial; the oil-finishing instructions are near the end in boldface type.

    If you find errors or have questions, please let me know.
  2. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA


    Although it is better to repair a broken or missing piece of wood with a scrap of the same species (preferably from the same board), “putties” can be used. Three different kinds are marketed:
    • Oil-Based
    • Water-Based
    • Solvent-Based

    Putties that use acetone-based solvents will begin to evaporate and harden as soon as the container is opened, despite your best efforts to promptly seal the container immediately after use; acetone is a highly volatile compound with extremely small molecules, and it is a tenacious escape artist -- it will find and escape through any irregularity in the container’s seal. Scrupulously cleaning the mating surfaces of the lid and container before resealing the container can help minimize these losses.

    Applying a layer of plastic wrap across the top of the can before reinserting the lid can help by acting as an additional barrier to prevent solvent from escaping.

    Some manufacturers (e.g., Woodpatch) place the labels on their cans upside-down to encourage consumers to store the product with the lid facing down, which helps thwart solvent evaporation. The instructor adds a small, sacrificial, quantity of acetone to the container before resealing, and stores his cans bottom-side-up. It is also helpful to write the date the can was opened on the bottom of the can with a felt-tip pen.

    If a previously-used can of putty has begun to dry out, it can often be rejuvenated if it is still pliable by mixing in additional solvent.

    Although putties are best reserved for projects that will be painted, stain-grade projects can include some putty if judiciously applied and finished. In either case, however, it is important to read the labels of both the putty and the finishing products to ensure they are compatible.

    A shop-made putty made from same-species sawdust and a few drops of finish (e.g., shellac) can be used in inconspicuous areas, however, the limitations endemic to manufactured putties pertain to shop-made putty as well. Shop-made putties using glue and sawdust are best limited to painted projects.

    Putties seldom match the color of the wood to which they are being applied, display completely different texture from the sourroounding wood tissue, and do not absorb stains and finishes the same way the adjacent wood fibers absorb them. Many wood species (e.g., cherry) change color with age, while putties do not. When putty is used in a project that will be stained, oiled, or otherwise remain visible when finished, a bit of camouflage can be achieved using artist’s brushes, artist’s colors, and stain, to emulate the coloration and grain patterns of the surrounding wood fibers.

    Putty can be difficult to apply without contaminating wood fibers in the area surrounding the repair. These smears will be visible when “clear” finishes and stains are applied. One technique that can minimize this kind of damage, is to apply blue painter’s tape before applying putty: When installing moldings that will be face-nailed and puttied, first apply painters tape, then nail through the tape, then apply putty through the hole in the tape. When the tape is removed, the area surrounding the filled nail hole will not have been contaminated by putty smears.

    Damage to a work piece during the construction process seems all but inevitable. A dent (compressed wood fibers) can be repaired by applying moisture and heat directly to the dented area, causing the wood fibers to swell and expand to almost their original volume.

    Start by lightly scraping the dent and the area immediately surrounding it. Then, apply a few drops of water directly to the dent and allow it to absorb into the wood fibers for a few minutes. Next, dampen a small area of a clean cloth and apply it directly over the dent.

    Using a clothes iron set to high, apply heat to the dented area through the moist cloth with the pointed tip of the iron, taking care not to press the iron into the wood. Avoid the temptation to lie the iron flat against the wood -- the objective is not to “iron the wood,” it is to apply heat and moisture only to the dented area in order to achieve localized swelling of the wood fibers.

    The instructor demonstrated this technique by inflicting four dents in a board. He then scraped two, leaving two un-scraped as a control. After circling the dents lightly in pencil, he steamed the dents. Those that had been scraped were virtually invisible, while the un-scraped dents were observable and could be felt.

    People tend not to notice perfection, but readily notice imperfections: an award-winning project depends as much on the avoidance of conspicuous faults as it does meticulous joinery and application of finishes. When a finish has been successfully applied, people will have an urge to touch your project; to have their sense of touch confirm what their eyes have observed, and to fully appreciate the tactile qualities of the surfaces.

    It makes sense for the artisan to employ these same senses during the finishing process. Use your fingers to inspect the prepared surfaces; can you feel defects or irregularities that may be observable when finish is applied? Using an inspection light at an angle to the work piece will cast shadows that will exaggerate surface imperfections; once found, they can be corrected.

    One of the most common finishing errors is the failure to completely remove mill marks before finishes are applied; these kinds of imperfections will be magnified when the finish is applied. This is because the scalloped surfaces presented by mill marks expose segments of end-grain which absorb stains and finishes at a different rate than face or edge fibers.

    While scraping or planing removes mill marks quickly, leaving a surface that is ready for 200-grit abrasives, the wood fibers are compressed and burnished to some extent (Tangentially, Japanese temple builders maintain their chisels and planes in such a super-sharp state that the wood fibers are compressed and burnished so effectively that water is repelled, making the application of wood finishes unnecessary).

    When finishes or stains will be applied, it is important to use abrasives after scraping and planing to prepare the wood fibers to consistently receive the finish. Abrasives cut across the wood fibers, creating a condition in which the wood surface is analogous to myriad wicks, thirstily absorbing stains and finishes, and allowing them to penetrate more-or-less evenly and uniformly.

    When water-based stains or finishes are applied, the wood fibers absorb the water swell, and the grain is raised, resulting in a rough surface. Deliberately raising the grain before applying water-based products minimizes this effect. After sanding through 220-grit, apply water to the wood surface and allow it to dry for 24-hours. Then, re-sand with 220-grit abrasive to remove the raised fibers, and apply the water-based product.

    A glue size (a solution containing 90% distilled water and 10% hide glue) applied before finishing can serve as a barrier coat that limits the absorption of successive finish layers, and can help reduce uneven absorption exhibited in end-grain and the blotching that can occur when stains are applied to certain species.

    The two oils commonly used in the manufacture of oil finishes are Linseed oil and Tung oil. Linseed oil is derived from the flax seed, while Tung oil is extracted from the nut of a Tung tree. Without further treatment, these oils would dry too slowly to make them suitable as wood finishes.

    Metallic driers are added to Linseed oil, which is then heated, resulting in a product commonly known as Boiled Linseed Oil. Tung oil is heat treated to achieve polymerization - a state in which the molecules are bound together in long strands.

    In 1989 the A.Q.M.D. (California Air Quality Management District) mandated changes to reduce VOCs (Volatile Organic Compounds) common in many wood finishes. These regulations resulted in the reformulation of many time-tested products that had achieved superior results as wood finishes, and stimulated the inordinate growth of water-based products.

    Prior to this time, Watco’s Danish Oil products were favored by many woodworkers for their ease of application, short drying times, and superior finishes. The reformulations mandated by the A.Q.M.D. in 1989 yielded products that were generally inferior to pre-’89 products and did not dry properly.

    After experimenting with many oil finishes in search of a product with characteristics comparable to the venerable Watco Danish Oil, Liberon Finishing Oil (a Tung oil-based product imported from England), was selected as the best oil finish.

    Minwax Antique Oil Finish (in the red can) also provides acceptable results, although it does not dry as quickly as Liberon Finishing Oil.

    Other Liberon products also work exceptionally well, including their French import Black Bison Clear Fine Paste Wax (available in neutral and several tinted shades), and their steel wool, an un-oiled product that is graded for consistent texture and scratch pattern, and is clearly superior to other steel wool on the market.

    NOTE: Steel wool should not be used in conjunction with water-based finishes, as steel particles will become embedded in the finish and will create unsightly black specks in the finish. When using water-based finishes, synthetic abrasive pads are available in several color-coded levels of abrasiveness. Scotch-Brite is one example. While bronze wool will not rust like steel, it is very fragile and disintegrates quickly.

    NOTE: An oil finish, while very suitable for the exterior of fine furniture projects, is not recommended for the interiors of cabinets, drawers, et al. Even with ample air circulation, an oil finish will not cure properly, and an unpleasant odor will linger long after the project has been completed.

    Before describing the process of applying an oil-based finish, a discussion of spontaneous combustion is warranted. Simply stated, spontaneous combustion describes [oil-soaked] materials bursting into flame: a very dangerous condition that should be avoided at all cost.

    Three components are required for combustion:
    • Fuel
    • Oxygen
    • Heat

    An oil-soaked rag item provides the fuel, and there is abundant Oxygen in the atmosphere. As oils polymerize, they generate heat. A rag lying flat readily gives off this heat to the atmosphere and combustion temperature is never achieved. However, in a folded rag or wad of steel wool, the heat is not allowed to dissipate -- it is contained in folds and pockets, and the temperature continues to build until combustion is achieved.

    Because spontaneous combustion is so likely, and the dangers so severe, caution should be exercised to prevent an occurrence. This is achieved by closely monitoring all oil-contaminated products during use (never leave an oil-saturated applicator unattended), and by promptly disposing of oil-soaked rags, unfolding them and spreading them flat on a concrete or dirt surface, away from all combustion sources, until completely dry.

    When the oil has thoroughly dried, you are left with a “rag Frisbee” that can be safely placed in a trash container.

    Each finishing session will require seven to eight hours when applying a hand-rubbed oil finish; between half-an-hour to an hour to apply and sand-in the oil, followed by six hours of monitoring and surface maintenance. This isn’t a project to start at 10:00 p.m. unless you are prepared to be up all night.

    Work on only one or two reasonably-sized surfaces at a time - don’t attempt to apply the finish to an entire project at once. One of the benefits of an oil finish is that there is no need to finish an entire project at once, or to maintain a wet edge. You can stop and start as you please, as long as you thoroughly remove all slurry before it dries and becomes thick and unworkable.

    After sanding to 220-grit, prepare silicon carbide wet-or-dry sandpaper in three grits:
    • 220-grit
    • 320-grit
    • 400-grit
    • 600-grit

    Tear or cut the abrasive into sizes that will be convenient and manageable when folded in thirds (I divide sheets of abrasive into eighths).

    You’ll also need to prepare an ample supply of clean, absorbent, lint-free rags with which residual slurry can be removed.

    Wet the wood surface with finishing oil, rubbing it in with your hands until the surface fibers are saturated. The instructor keeps his finishing oil in a squeeze bottle (with an airtight lid), for easier and better-controlled application.

    Start with 220-grit and sand the oiled wood, with the grain, until a slurry of oil and sawdust is created. Once a slurry has been created you can sand in circular or figure-eight patterns. Work one small area at a time, until the surface is consistently smooth and the slurry has been packed into the open pores of the wood.

    After perhaps ten or fifteen minutes, the surface(s) you have been working will be consistently sanded to 220-grit, and the slurry will have begun to thicken. Now it’s time to wipe all remaining slurry from the surface of the wood with a clean rag. The instructor uses manicurist’s orange sticks, wrapped in a clean cloth, to remove all traces of the slurry from corners and areas containing detail and tight radii.

    This needs to be accomplished before the product becomes too dry and gummy to remove easily - with Liberon Finishing Oil, you have about twenty minutes. With other oil finishes, such as Minwax Antique Oil Finish, you have a little longer - perhaps three-quarters of an hour.

    You will need to monitor your project for bleed-back over the next six hours. Bleed-back is the term used to describe residual oil that will ooze from the wood pores up to the wood surface as the finish polymerizes. Bleed-back will appear as small bumps of finish on the surface of the wood.

    Inspect your work once an hour, wiping away bleed-back with a clean rag. Then allow the first coat to dry for 48 hours before proceeding.

    When you have sanded the oil finish into the entire surface of the project using 220-grit abrasive, repeat the process with 320-grit. Wait twenty-four hours and repeat the process with 400-grit; after another twenty-four hours and repeat the process with 600-grit. Allow at least seven days for the finish to cure before applying two thin coats of hard paste wax containing Carnauba wax.
  3. Greenman


    Dec 17, 2005
    Ontario Canada
    Good post. Similar to the way I hand rub. I learned a few things. :)
  4. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    Thanks for the tutorial.

    It is similar, with a few differences, from the one I've seen quoted before. It's great to have another view by someone with experience.

    I've got a question about the oil slurry method. Since the pores get filled with sawdust/oil, as opposed to transparent finish material in more conventional methods, what is the effect on shininess and "picking up the light", or especially on chatoyance of flamed woods? And, what's the effect on end grain?
  5. Greenman


    Dec 17, 2005
    Ontario Canada
    I've read in books some will not use this method due to clouding the finish.
  6. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA
    Thanks for providing the link.

    First, I should note that the Liberon Finishing Oil I prefer to use is an oil and varnish blend and not straight oil, which cures too slowly for my preferences and doesn't provide the sheen or abrasion resistance of varnishes and oil/varnish blends.

    I've used this method with several different finishing products, including linseed oil, tung oil, mineral oil, Danish oil, wiping varnish, regular alkyd varnish, urethane varnish, and gel urethane (among others).

    I haven't had any problems with cloudiness or undesirable opacity using Liberon, wiping varnish, regular alkyd varnish, urethane varnish, or gel urethane, all of which provide ample sheen and protection when properly applied. I haven't been nearly as satisfied with thin-bodied products and straight oil.

    End grain is sealed by the vigorous wet-sanding, yielding an appearance that's more consistent with face and edge grain than I've found using many other finishing methods, even with ring-porous species like oak and ash [You can see the endgrain of the cutting boards in one of the snapshots]

    I've experienced no reduction/flattening of figure or chatoyance. I have a modified method that I've used to pop figured maple and burled woods, but that's a song for another set.

    One potential downside to this method is that, when different species have been married in the same project, the slurry will become colored, which can fill the pores with sometimes unpredictable tonal variations. This is particularly observable with species like padauk and ebony, although the effect can be stunning in some applications.

    I'll see if I can attach a few snapshots showing work that received a sanded-in oil finish using Liberon Finishing Oil.
  7. treebranch13


    Oct 31, 2007
    does this affect sound at all? does it change color of the wood at all?
  8. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    Beautiful stuff!

    I think the drummer just got back from having his smoke. So, you were saying...? ;)
  9. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA
    In addition to the normal "ambering" that results when oil-based products are applied to wood (IME, linseed imparts a slightly darker shade of amber than tung), the sawdust and oil slurry can sometimes change the color of the wood when different species are combined (I cited ebony and padauk as examples in my post, above).

    I have heard absolutely no change in sound relative to any of the other finishes that are typically applied to solid-bodied electric basses.
  10. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA
    Do you know how you can tell when the stage is perfectly level? There's drool coming out of both sides of the drummer's mouth ;)
  11. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    What do you call someone who always hangs out with musicians but knows nothing about music?

    Groupie? Nope.

    Drummer. ;)

    But anyway, special method for popping the figure?
  12. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA
    It's not complicated, but it does take some experimentation:

    Prep the raw wood, and inspect the surface for errant scratches and other defects by wiping it with a rag dampened with mineral spirits and examining the surface with an inspection light held at a low angle to the work piece; then allow the wood to dry completely.

    Apply aniline dye (I like Transtints because they're resistant to UV fading, and because they can be mixed with water, alcohol, or solvents) and wait for the surface to dry completely.

    Sand thoroughly to leave the dye in the dense figured tissue and remove it from the softer surrounding wood fiber (If you don't like the color, you can usually remove it using household bleach before sanding).

    IME cool colors (blues, greens, purples) tend to blend figure with surrounding wood fiber, making it less conspicuous and creating a more-or-less homogeneous appearance, while warm colors (yellows, oranges, reds) tend to "pop" the figure and heighten contrast.

    It's important to realize that dyed wood often looks like a failure - drab, flat, two dimensional - until the clear coats have been applied: I always encourage my students to complete all of the steps in the finishing process on each test piece before being tempted to render judgements about appearance.

    Compatibility of finishes is an important consideration. For example, I will sometimes use shades of yellow/orange to pop the figure in mahogany; I have to be careful not to bury it under a finish like orange shellac, which will make it blend in and disappear. When an amber clear coat is undesirable I use a "water white" (clear, non-yellowing) water-borne top coat like polycrylic; this can be an especially important consideration when clear-coating white and cool colors.

    I find that rubbing out the finish helps pop the figure (irrespective of the sheen level) because rubbing-out reduces distractions caused by surface irregularities, and heightens the perceived clarity of the clear coat.

    Dying and wet-sanding aren't always compatible. Applying an oil finish over dyed wood introduces several new variables because of the likelihood that sanding-in a finish will liquify and remove at least some of the dye, and because of the ambering introduced by oil finishes. When dying burled wood, instead of applying a sanded-in oil finish, I will sand to pop the figure, and fill the open grain and the voids and with epoxy, which also seals the wood, locking in the dye.

    FWIW, I list all of the products, the quantities and proportions used, and the exact finishing process followed, on note cards that I affix to the back of each test piece. This enables me to make educated guesses about what went wrong, take note of the effect subtle changes can make, and repeat successes when things work out well. When I make changes, I change only one element at a time so I'll know how each change effects the final finish.

    OK, now what have I forgotten? :meh:
  13. Great tutorial! I hope it will become sticky.
    I loved the pictures of your works - I didn't expect oil finishes to be so shiny. Is it hard to maintain it in that condition?
    Thanks for aniline dye hint - I don't expect the natural color of my bass to be very spectacular. I'd rather go red or dark brown (the current finish colour). What solvent will make the dye go deeper into the wood? Is alcohol OK?
    You advise not to finish all the project at one time. Does it mean that I have to apply finish to a single surface, let it dry and then go to another surface? May the whole piece be oiled surface-by-surface and then let for drying?
    Sanding sequence isn't clear enough to me - did you mean 4 oil "coats" are to be applied using a finer grit paper for each subsequent coat?
  14. Very useful info, thx, really helped me improve the finish of my current build. I apply danish liberally with a rag first, then leave to soak and dry for 24 hrs before doing the wet sanding/slurry method with 400, 800 then 1200 grit wet'n'dry, leaving each time a day to harden. You can see when the pores are starting to fill up as each subsequent coat of danish goes further, ie: absorbs less. I end up with a gloriously smooth silk finish then buff up with good furniture wax. It's given the Zebrano a great golden lustre - without the oil it can look cold and grey when finish-sanded.
  15. Greenman


    Dec 17, 2005
    Ontario Canada
    Thanks for taking the time to share. My current project will be rubbed linseed oil and will use the raw linseed oil to fill which takes longer.
  16. Jazzdogg

    Jazzdogg Less barking, more wagging!

    Jul 29, 2006
    San Diego, CA
    I'll try to answer your questions in the order you asked them:

    The sheen is as much a function of the product used as technique; part of the sheen is also attributable to a few well-buffed coats of Liberon Black Bison paste wax applied after the finish has had time to cure completely.

    One of the reasons I favor varnish and oil/varnish blends is because they give me the option of a gloss or semi-gloss finish if that's what I'm after. Products with a low solids content take far more coats to achieve a shiny finish. Maintenance is also a function of the solids content of the finish. IME, light-bodied finishes require perpetual maintenance, whereas varnishes and many oil/varnish blends require little or no additional maintenance.

    I've attached before and after snapshots of the same mahogany bass. The before photo shows how the factory-applied oil finish had begun to degrade after a few months. The after picture (on the right) shows the same instrument after I did a bit of recontouring and refinishing. It looks pretty much the same now, after several years of gigs, as it does in the snapshot.

    I usually recommend distilled water as a diluent for hand-applied Transtint aniline dyes because some species, e.g. oak, that have a naturally high tanin content may react in unexpected ways to tap water with high concentrations of dissolved iron; alcohol and most solvents are great for experienced finishers - especially when spraying, but water gives you more time to even-out the color coverage before it evaporates.

    The reason I recommend working one reasonably-sized area at a time is to make the job easier: it's easier to rag off the slurry before it has stiffened up too much.

    In answer to your final question: Yes, I sand-in four separate coats of an oil/varnish blend, each one day apart. Each coat is applied with a finer grit of wet-or-dry abrasive; I start with 220-grit, followed by 320-, 400-, and 600-grit. That being said, on ring-porous species like oak, I will sometimes apply the first two coats using 220-grit because it generates more sawdust and fills the large pores more quickly than 320-grit would.

    I try to let the wood absorb as much oil as it will take before I begin sanding. I'm not reluctant to add a bit more oil while I'm sanding, because I want the oil to penetrate the wood as deeply as possible. IMO, using too little oil is a waste of time; if I'm going to expend the effort, I might as well achieve the best coverage and penetration possible. OTOH, if you use too much oil, you can wash away the slurry, instead of forcing it into the pores.

    As always, I recommend you "test drive" the process using scrap of the same species as your bass instead of learning on a valuable instrument. If you don't have any scrap, you might want to perfect the process on the back of your bass before you start finishing the side the audience will see. I do not recommend combining dyes with a sanded-in finish unless you have a chance to do a lot of experimentation first because it's really easy to screw up without sufficient practice.

    If you want to change the color of your bass AND use a sanded-in finish, I've achieved good results by wet-sanding gel stains in lieu of an oil/varnish blend, followed by several coats of clear finish.

    Good luck :D
  17. treebranch13


    Oct 31, 2007
    Will it always make a brighter color or could you make it have the same or darker color too?
  18. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001

    I was under the impression that raw linseed oil never dries/hardens. Is that right?
  19. Jonsbasses


    Oct 21, 2006
    Fort Worth, TX
    Builder: Jon's Basses
    If it does, it takes many many weeks to cure. I know boiled linseed oil does, but it contains chemicals to make it cure.
  20. Greenman


    Dec 17, 2005
    Ontario Canada
    I even thin my raw linseed oil with about 15 percent turpentine sanding the "fuzz" off with the slurry method. Then I don't use that method anymore. Once the wood stops absorbing the raw I wait a bit and continue with double boiled using pressure and heat hence hand rubbed.