Black Stains on Curly Cherry Veneer

      Figuring out the source of discoloration on a beautiful figured cherry veneer. June 28, 2006

I have successfully laminated 17 surfaces of curly cherry on four speaker enclosures using Titebond Cold Press Veneer PVA. With three surfaces to go, the 18th had black stains in one corner, say 15% of the surface area. It is in the picture. The one thing that I did differently with this panel was leave it under pressure for 18 hours. The others usually were pressed for 6 hours. I presume the stains are mildew from closed exposure to the water in the adhesive. But why on only one corner of the panel? I tried scraping it away with a cabinet scraper. Some of it comes off, but the three worst splotches look too deep to scrape entirely away. Are there any other methods of removing the mildew but retaining the colour in the veneer? Of course, all 20 panels on the speaker enclosures are matched.

Forum Responses
(Veneer Forum)
From contributor K:
I'm not sure that mildew could grow without air. I'm wondering if there may have been some contact with steel stain. If that is possible, I would try the oxalic acid type wood bleach. It will remove the stain without bleaching the wood.

From the original questioner:
Thank you for the insight. I agree with your analysis that the stain is probably some kind of iron, tannin, water reaction. I am befuddled as to where the iron/steel could have come from. The veneer has not been sanded, of course. The platen was melamine. Surely it can't preexist in the veneer.

At any rate, I took a cabinet scraper to the veneer (what did I have to lose?) and I have been able to remove enough of the stains to make the panel usable without breaking through the cherry, so life is good again. Thanks for your help.

From John Van Brussel, forum technical advisor:
Most likely this is blue stain, which is caused by metal particles being oxidized by the veneer. It could be from steel strapping, the knife used in cutting, the dryer screens or any other metal object which contacted the veneer.

From contributor J:
I don't know how you can say that no air (oxygen) is present during any process. If there was no oxygen, nothing would set up properly. The source, although I agree that it probably isn't mildew or mold, could be any number of things. I don't believe you saw the marks prior to layup, so I'll discount ink or sticker or mineral (spalting marks) during harvesting. Sometimes lead in the tree from bullets will show up as these kinds of stains - you can see that not only is it in the spots, but is also incorporated in the figured grain, so that might have been in your veneer and you did not notice it until water was added. I have seen this many times before and I still haven't tracked down the source. If you're using a press to lay these veneers up, could be file shavings or contamination from that. If I were to guess, I'd say this is from when the tree was growing.

Did you make a mistake referring to this as curly cherry? It sure looks like figured maple to me! Maybe this cherry has Vitiligo!

From contributor A:
I get this problem with cherry and quilted maple. It is mold, and oxalic takes it away. Try letting the glue film over so it doesn't saturate veneer, or train a fan on the curing sandwich, or use glue with no water (polyurethane) - the best solution. More of a problem in higher humidity.

From contributor F:
The veneer is definitely curly cherry. I had never seen it so figured before, either, but I am new to veneer and have much to learn. But I do know cherry in its hardwood form.

Thank you all for the information. I did not realize contamination could occur from so many sources. It was a great education. I did manage to clean up the splotches and did not incur any others on the last two panels.

Here is a picture of one of the speakers with only the veneer finished so that you can see the curly cherry effects, although some of the colour of the aged cherry was scrubbed off during the finishing. The front baffle, with no drivers mounted, is fresh cut quartersawn cherry and hence has the pink colour instead of the cinnamon rusty brown of aged wood that has been exposed to light.

Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?

Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Knowledge Base

  • KnowledgeBase: Veneer

    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.

    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2016 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB

  • WOODWEB - the leading resource for professional woodworkers

      Home » Knowledge Base » Knowledge Base Article