Official Luthiers Forum!

Here is a problem for all the experts. I recently bent sides of Alpine Ash (Eucalyptus Delegatensis) with added moisture (not soaked but wiped on) only to fine that the interaction between the timber and the side material produced some blue/black spots. I then bent the side without any added moitsure and the problem was resolved. Some I have spoken to over here mentioned that a specific type of paper has been used with timbers that have a tendency to do this. Any thoughts?

regards

Tim

Blue black spots


Clear surface. There was no spotting on either side.

   There are times when you get a reaction. Often it is water chemistry and a reaction to the woods resin or just something that happens.
    I use Kraft paper when I think I have wood that will stain. I have had Maple and Koa both stain. Since then I started using distilled water and that helped .
     Stainless steel slats tend to be the better option for non staining. Spring steel you will \need a barrier and depending on your water chemistry aluminium can also do some staining.
     I have found too much water is more of a problem than not enough. Wood is thermoplastic and will bend with heat. Moisture is more for air density and anti scorching.
    I have found most staining sands out pretty easily. Of the one set of Koa I had turn green , a nice stain job took care of that.
Have fun
john hall

I have had the same problem with Maple, I assumed it was either my tap water or the steel slats I was using. Using distilled water I still got the staining, so now I have to assume it is the steel slats.

Using parchment paper (a silicon impregnated paper) between the wood and the steel slats keeps the staining from happening. I think some people wrap their sides with aluminum foil as well, but I have not tried this as I would think it difficult for wet sides to release their water if wrapped up in foil.

^ Oops I wasn't finished typing yet. I was going to add that my results are somewhat anecdotal as the results were not from the same board. There may be some compound in some maples and not others which reacts with water, heat, and/or pressure to create the spots.

Either way I would recommend that you bend your sides a little thick if you think there's a chance of this happening so you can sand out the spots if you need to and still have plenty of side left.

Thanks Lex.

I think some people have been using a particular paper from some of a couple of the big suppliers.

Tim

I see a grinder in your photo. Micro iron filings on your wipe down cloth from contamination surrounding your grinder area is my guess.

Dean

_________________
Dean

   The Silicone is a NoNo. Kraft paper works as well as anything as is similar chemically to wood. If you are using stainless steel you shouldn't have any issues there. If you are using tempered steel or High carbon steel you will get the staining from ion transfer.
   The iron itself will migrate from the steel into the wood and this is most difficult to remove
john hall
blues creek guitars

The side set was transfered from the sander to the bender with only one temporary stop on a set of chrome rollers. The slats were stainless steel so I am guessing that there was some interaction bewteen the additional moisture and chemical in the wood. THanks for all your thoughts on the matter.

regards

Tim