Gazette Archive 7/19/99
Woods and Endgrain
Evening out the finished color of wood can be difficult because some species have random, ugly dark blotches that come from uneven stain absorption. Endgrain will also soak up way too much stain and look unsightly, too. This is a quick look at some ways to achieve even coloring by preventing or getting around color absorption problems.
In attempting any of the following procedures below, be sure to wear eye protection and protective gloves. Otherwise, you are exposing yourself to unnecessary risk. When using some products like lacquer, additional protection is required - see the manufacturer's MSDS and tech sheets for proper handling and safety measures. Read and follow all product labels with regard to additional safety information. Wood finishing is an inherently dangerous pursuit.
Most of the workarounds presented below have shortcomings, mainly that all of them involve extra cost or extra effort. None are a complete guarantee against blotching, but they do represent a big step towards a great finish.
Workarounds for coloring blotch-prone wood:
No matter which of these you select, be sure to TEST the effect on scrap before you attack your project. You may need to use more than one method to get premium results.
The best product for washcoating is blonde dewaxed shellac. Use one-half pound cut shellac. Most canned shellac is not dewaxed and flake shellac almost always indicates on the label if it is dewaxed or not. Pound cut means that you have x lbs. of flakes in 1 gallon of solvent.
To mix a small amount of flakes to approximately this concentration, try:
1. Get a clear glass jar. Make a mark
about 1/3 of the way up the side of the jar. Make a second mark
about 2/3 of the way up the jar. Fill the jar to the first mark
Most canned shellac is 3 pound cut. Simply dilute the shellac 1 part shellac to about 5 parts solvent to get pound cut. Be sure to dewax the canned shellac. Let it sit for 2-3 days, then decant off the clear stuff. The cloudy stuff at the bottom is wax. Pitch it.
Apply the shellac with a soft rag, let it dry for about 2 hours, then sand lightly with 220 grit paper to remove nibs. Remove the dust. Apply any stain or dye, even water-base products over the shellac washcoat. Follow the product label instructions for raw wood.
The idea here is to seal the surface with a clear coat of lacquer, sealer, or shellac. Then, apply several light coats of toner until you have the desired color. If enhanced grain is required, then try a drying oil as the first sealer coat (to pop the grain), and then apply dilute shellac as a barrier coat followed by toner coats. Examples of drying oils are tung oil and boiled linseed oil.
Seedlac - dark brown
Note: the colors of these grades vary from supplier to supplier. The color strength per coat is not that great, so several coats are almost always needed - an advantage.
Also, consider adding SMALL amounts of alcohol-soluble dye to any of the above grades of shellac. This allows you greater flexibility in color control, in case you need to match an existing color.
Be sure to dewax the shellac first. Then
brush it on at about a one pound cut.
This works especially well for cherry, which already has some color and requires fewer coats to get to a reasonable color than lighter woods like aspen and pine.
Glazing stain is available either as either pigmented or natural color glazing stain. Add wetted pigment to the natural glazing stain if you need a color that is not available off the shelf. Wetting pigment means pre-mixing the pigment in the appropriate solvent before it goes into the glazing stain. Mix pigment and thinner into a thick slurry or thin paste, then slowly stir the goo into the glaze.
Glazing is very easy, and completely reversible. Apply the glaze evenly to the surface with a cheap brush. Let the solvent flash off for about 5-10 minutes. Then, start wiping away color with a coarse rag until you get the look or color required. If you don't like what you have, you can wipe off all of the glaze and start over. No harm done.
You can also even out ground color differences in the glazing step, by removing slightly more or slightly less glaze in certain areas. This is best achieved by using a dry soft brush to lift off small amounts of glaze in small areas. Keep the brush clean by wiping off glaze buildup frequently.
Let the glaze cure for a few hours, then apply the shellac barrier coat, then several clear topcoats. Glaze is really intended to darken already existing color, not create all the color by itself. Consider adding a little base color to the finish at some earlier step if you want the glaze to be more effective. Really thick glaze is opaque. Thin glaze works much better in my opinion.
'Sunburn' and lye application are two
ways to simulate the effect of aging on cherry.
Raw cherry will 'sunburn'. Work only with unfinished wood. Direct sunlight causes blistering in new finishes. Be sure to provide a way to allow complete, even exposure of the piece to sunlight. 3-4 hours exposure in midday sun is the maximum required.
Cherry also darkens on exposure to a strong base like lye (sodium hydroxide). Brush on a weak lye solution (1 tablespoon of lye per quart of water). Let it dry. Wash off with water, then neutralize with a solution of vinegar (3 tablespoons per quart), then wipe clean. Let it dry. You will get slightly different results on different pieces with this procedure, as it is hard to standardize. This procedure also raises grain considerably. Consider sponging and sanding prior to applying lye to eliminate grain raising problems. You can repeat the process for more darkening, if needed.
Most species of wood will react to a potassium permanganate solution by turning various shades of brown. This method is similar to using lye on cherry, but doesn't require neutralization.
You can add tannins to any wood by drenching it with a strong tea solution. After the solution dries off thoroughly, wipe it down with a dilute iron acetate solution. This will create some wonderful colors, especially in pine. Colors range from silver gray to dark black-brown, depending on the concentration of the tannins. To make iron acetate, soak oil-free steel wool in a white vinegar solution (1/4 cup vinegar in a quart of water) for 2-3 days.
Old Growth has several stains and 'aging' agents for wood. There is a mineral solution followed by a catalyst solution. This system works well for creating different effects and behaves somewhat differently with each species of wood. It also creates color several millimeters deep into the wood, which most other treatments and finishes do not accomplish. This means you can still sand somewhat aggressively after coloring with this product. It is a rather pricey product, however.
All of these chemical treatments work on raw wood only. Further finishing steps need to follow for a good quality finish.
There are two classic ways of slowing down absorption of color into endgrain:
Dilute linseed oil
Editor's Note: Jim started working on wood in his grandfather's church furniture shop at age 13 and learned wood finishing there from the shop's head finisher. He went through college in Wood Science and taught at college for about 10 years. He's been in woodworking for about 40 years.
Jim live's in New Mexico on the Santo Domingo Reservation where they build reproduction Southwest furniture and try to duplicate old finishes, sometimes with materials like amber or turquoise. They also do refinishing work.