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Thread: black spots on maple bowl

  1. #1

    black spots on maple bowl

    Hi all,

    My first post here. I have recently (March) started turning wood and am loving it. I've had good success and have really enjoyed every aspect of learning this new hobby including the finishing. I have just recently had my first experience where I am totally stuck. Here's the situation:

    I turned a nice red leaf maple bowl, sanded through the grits to 600 (using Vince's abrasive discs and a close quarters drill). Then I used EEEUltrashine, which has given me very good results in the past. My intent was to use a friction polish after the Ultrashine.

    Unfortunately, this was the stage that I noticed some sanding lines under the rim of the bowl. No problem, I thought, I just went back and re-sanded, this time by hand, starting at 100 up to 220 grit. Bowl looked nice and smooth.

    At this point, I decided that I would just use a waterbase poly because I liked the light color of the wood. I have had good luck with this as well. So I went to the first step of this process which is to spritz some water on the bowl to raise the grain and dewhisker it after the water had dried. Unfortunately, when I sprayed the water on, I immediately noticed these bluish/blackish streaks. Looking closely at them, they are actually little black dots. The weird thing is that the inside of the bowl and the bottom of the bowl are just fine. But the outside of the bowl is covered with them. It's most prominent on end grain areas but is not limited to these. If I let it dry, the spots go away (mostly). But as soon as I put any solvent on the bowl, whether it's water, naptha, mineral spirits, the spots come back. So I don't know what to do about finishing it. And I'm stumped as to what's causing it.

    Any thoughts and advice would be most welcome.

    Thanks very much


  2. #2
    Join Date
    May 2008
    Olympia, WA
    Might be iron. Maple is real sensitive to iron staining. Maybe specks from the sanding or workshop?


  3. #3
    Dan, How wet was the wood when it was initially turned? Do the spots go away when wiped with some lemon juice or bleach? Does spritzing with DNA (vice water) to see if that makes a difference.

    Also, a nearby grinding station can put fine metal particles in the air which might be getting on your wood. Try moving grinder further away from lathe, and keep your dust collector running between your lathe & grinder whenever you sharpen. Just be careful not to vacuum up any sparks coming off the grinder.

  4. #4
    Wes, Karl,

    Thanks for the replies. I was not grinding anything around this bowl, although the band saw that I used to knock the corners off the blank may have had a little rust on it. The wood is kiln dried. I will try lemon juice and bleach and DNA, those are all good ideas. I actually thought about using wood bleach on the whole bowl and going for a sort of pickled look. Frankly part of me wants to just toss the piece and move on but I'm stubborn and I sure would like to figure out what's going on.

  5. #5
    Join Date
    Aug 2007
    Lakewood, CO
    Can you post a picture of the spots?

  6. #6
    Most likely from metal dust, especially since you used a water based finish on it. Try a little concentrated lemon juice on them to see if that takes it off. I run into this a lot, but not as much as I used to because I try to prevent it now. You can have dust on your hands, and your tools after sharpening, or even just putting your hand down any where near your sharpening area. I don't think it is a problem from the air born metal dust though. Some times there is mold, more so on maple than other woods because of the sugar...

    robo hippy

  7. #7
    Pat, will post some pictures later today.

    Robo, thanks for the tip. I’ve learned a lot watching your videos.
    Last edited by Dan Gaylin; 11-02-2018 at 4:41 PM.

  8. #8
    Okay, here are some pics. Lemon juice didn't do anything. Bleach might have lightened the spots a little. Thanks again for your help.


  9. #9
    Join Date
    Aug 2007
    Lakewood, CO
    As I was looking at the pictures I was thinking the wood must be Maple because I've turned Silver Maple before that looks like that with dark spots. Sure enough I scrolled back up and read again this is Red Maple. My Silver Maple bowls look "dirty" but there's nothing you can do, or at least nothing that I do but chalk it up to that's the way this particular piece of wood is.

  10. #10
    Thanks Pat. That is reassuring. Also a bummer. I’ve turned several pieces of hard maple with no problems. Guess I will stay away from red maple in the future.
    Last edited by Dan Gaylin; 11-04-2018 at 11:42 AM.

  11. #11
    Join Date
    Mar 2016
    Elmodel, Ga.
    Dan, I do a good amount of segmented bowls and have had the same issue at times. I think it's just the nature of the wood. It can be aggravating to have a piece look totally perfect except for one segment that came off the same stretch of wood that has some black spots of streaks in it after finishing. Most recipients of the bowl don't mind it saying it gives the bowl some character. I've got to learn to quit being a perfectionist when turning. Wood is fickled and each peice is unique.

  12. #12

    Thanks for for your reply, much appreciated. I read it to my wife and she chuckled because the last bit about letting go of the perfectionism is something she keeps saying to me. Good advice!


  13. #13
    The first pictures did look like metal dust spots. The last pictures look like mold. Maple is prone to this because of the sugar in it, I guess anyway. I found out a long time ago, with my stretch wrap around the rim, that it doesn't work well for maple because the mold appears under the plastic. Since maple is generally fairly stable, and not as prone to cracking as other woods, I can dry my maple bowls without the wrap. If you are twice turning (rough out, dry, then turn again) you could run into those mold spots under sealers, but I don't know since I don't do that. I don't think that type of mold comes out.

    robo hippy

  14. #14
    Join Date
    Jan 2010
    Midland, MI
    I agree the later pictures look like mold. I've not found a way to remove mold once it's started.

    For me, maple that was cut in the spring or early summer has been very prone to developing mold spots. Trees cut in late fall/early winter, when the tree is dormant, have much less tendency, I suppose due to less sap/sugars in the wood and due to the colder temperatures in my garage where I store the wood prior to turning.

  15. #15
    Access to Sugar Maple out here in Oregon is very limited. The only tree I got was good sized. I left a good section of it out in the Oregon Rain because I knew it wasn't going to check very much with 100% humidity. When I got around to turning it, it wasn't molded, but the color was very dull. I had some one once tell me the same thong about Silver Maple, that if you let it sit, it will lose all of the shine and brightness of fresh cut wood. I would expect that this is again caused by the sugar in all maple trees. I guess we can make maple syrup from the Big Leaf Maple out here, but it takes several more times the amount of sap to boil down than the Sugar Maple sap.... If I ever get another sugar maple tree, I will process it ASAP.

    robo hippy

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