How to color epoxy for knot filler?


I'm using some highly figured cherry as the top of my daughter's sideboard. There are a couple small knots which I would like to fill to smooth the top and avoid collecting dirt. I'm not trying to hide the knot, just fill it. I recall Norm used epoxy to fill some knots (in mesquite?) on a project, but I do not think he explained what epoxy he used or what he used as a coloring agent. As I recall, he colored his epoxy black, while I'm looking for a dark reddish brown. Anybody have any experience with this or an alternative method?
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Larry Kraus wrote:

Yup.
I find that black works best, as counter-intuitive as it seems. Other colors seem to end up looking un-natural after the entire finishing process is completed. I've used everything from universal tints, to kiddie tempera, to artists acrylics to tint the epoxy.
Try it on some scrap and see.
Don't forget to scrape or plane the hardened epoxy, as opposed to sanding it off, for better results.
Barry
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I've used small tubes of artists acrylic paints (local art store) and found that "Burnt Umber" alone worked well for walnut and with a dab of "Mohave Red" as I recall - it worked nicely with cherry. There's usually a chart of samples at the display so pick a dark red and add a very small amount of the burnt umber and I think you'll get a color that will look good. Match the color of the knot - not the surrounding wood. Hard to give you a ratio of color to add to the epoxy but something like 1 part color to 50 parts epoxy will give you an idea that a dab of color goes a long way.
As for mixing with the epoxy and color. Premix the artists colors until you get what you want. You will only need a small amount to color the epoxy. I used the two part (5 min setup) stuff and mixed it as per directions then added color while stirring it to blend it in. You'll know how much to add by seeing that the epoxy doesn't change color any more. Remember that the epoxy will add a bit of a shine to it so you'll sand that down to dull it before applying the finish coats - even if it's a gloss finish. If the epoxy is not even with the surrounding wood - it will be noticeable, so add a bit more and then sand it flat.
Bob S.

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wrote:

I use artist's acrylics for colouring, but it's also important to use a soft filler, like phenolic microballoons. Unfilled epoxy is brittle and hard to level, the filled stuf is not only easier to smooth, but it gives better edges too.
As the phenolic filler is already a reddish brown, most timbers need a little green or even yellow to give a good match.
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Larry Kraus wrote:

I have used sawdust from the wood itself as a coloring agent for filling epoxy knot fills. It comes out a little darker than the surrounding wood, but so do natural knots. Just remember to scrape the surface of the epoxy after it is dry to avoid an artificial glossy appearance.
HTH
Godzilla
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Since my original post I've experimented a bit. I had some SuperGlue brand slow set epoxy that is a clear, amber color. I tried a bit in some scrap and found that the dark color of the knot shows through the epoxy pretty well without being too dark. I overfilled the knot a bit and then trimmed it down with a block plane and hand scraper after it set. It seems to require careful mixing to avoid air bubbles, but most of those I had seem to work their way out before the epoxy set hard.
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You can also lay down epoxy and use it to adhere more bark - either ground, or in chunks - to the recess. That way the bark is on top accepting stain/finish the way bark does, not the way plastic does.
Sawdust looks like dead fish eyes.
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Larry Kraus wrote:

I use a lot of epoxy building a boat.
About the only color you can rely on is black.
A qt of black pigment is about $10.
A dollop the size of a tablespoon will color about a gallon of resin.
When it comes to furniture, epoxy can be a real PITA for other than adhesives and black filler for mesquite cracks.
For covering a knot, have you ever considered a "Dutchman">
They can be very creative and quite attractive.
Lew
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In addition to the suggestions the other offered you can also usually get pigment from whomever your local seller of fiberglass/composite boat building supplies. The same pigment is used to color fiberglass resin. I usually add some additional filler material to provide some strength, reduce shrinkage and make it a little bit thicker. Milled glass fibers, "micro balloons" (microscopic glass beads), and talcum powder are the most common additives and usually can be purchased the same place as pigment. There are also numerous sources of this material on the web as well. Many of the outlets have information on how to mix and use the products available for free online or as flyers in their stores. good luck, Joe.

Joe Brophy CountryTech Computer email: snipped-for-privacy@spiretech.com
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Larry Kraus wrote:

In addition to the other suggestions you've received, there is a product called "Apoxie sculpt" (http://apoxie.sculptingstudio.com /). It's a moldable, putty-like epoxy compound that comes in various colors. I don't know that you could get a color to match, but I think black looks better anyway.
I've used it to fill knotholes and wormholes in mesquite, and I'm happy with the look. It's easy to work, and not as messy as epoxy.
I've played around with various methods, including doing a turquoise inlay (that's very popular down here in Texas), but I now prefer just filling with clear epoxy. I fill in two steps; first fill just below the wood's surface, let dry, and then come back and *slightly* overfill (see below) and scrape flush when dry.
The whole operation is easier and neater if you use blue masking tape to surround the void being epoxied. As soon as the epoxy is in place and leveled, remove the tape. If you fill to flush with the surface of the tape, you'll have just a tiny bit of epoxy to remove with a scraper.
Chuck Vance
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