After I rough turn green wood and let it dry for a final turning, somtimes spalting starts to set in on some pieces. The wood is usually pretty green (wet) when this happens. I sometimes like to put rough turned bowls of a species into a large box and rotate them around once in a while. But if I have to leave them unattended for any period of time, mold sometimes grows and spalting starts. It usually goes from one side, through the thickness of the bowl and can be seen on the other side as well. I travel a lot and sometimes rough turn a bunch of stuff before I leave only to comeback and find grey discolorations on part of the bowls. I am sure being that they are so wet has much to do with this problem but then again I do not want too much air to get to them so they crack. Two questions: How can this be prevented? .....and.. Is there a good way to bleach out a finished turned piece so coloring is consistent across the entire bowl? Thanks much for any input.....
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Prevent/Fix Unwanted Spalting?
- Thread starter John Chianelli
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Hello John,
First off, to what types of wood does this happen?
Secondly, you are going to have to experiment for a short while. I agree, you need to speed up the moisture evaporation from what you have now, but not so much that it causes cracking. The box method is likely holding too much moisture for the location. Can you move the box to a drier location or increase the air circulation around the box?
An alternate route is to find another material to place the roughouts in that has more breathability. Maybe paper grocery bags. Or perhaps the "old timer's" method of burying the turnings in a pile of shavings.
It's going to take a little experimentation to find the right combination for your woods, geographic location and the micro-climate of your home/shop.
Owen
First off, to what types of wood does this happen?
Secondly, you are going to have to experiment for a short while. I agree, you need to speed up the moisture evaporation from what you have now, but not so much that it causes cracking. The box method is likely holding too much moisture for the location. Can you move the box to a drier location or increase the air circulation around the box?
An alternate route is to find another material to place the roughouts in that has more breathability. Maybe paper grocery bags. Or perhaps the "old timer's" method of burying the turnings in a pile of shavings.
It's going to take a little experimentation to find the right combination for your woods, geographic location and the micro-climate of your home/shop.
Owen
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Black mildew. Nasty stuff with deep footprints. When I did the wet shavings in a bag routine it was always there, and when I coated the wood, it was the same. Finally realized that the conditions OUTSIDE the bag or occlusive covering were stable and damp enough to do without either. If you're doing shavings in a bag, use dry ones to help buffer your piece down, and change them after no more than a week. I prefer open storage.
First, get a hygrometer or two and find out what your relative humidity runs in places where you might store your roughs. Second, take a look at chapter 3 here http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm to find out what that RH translates to in MC. For the type of roughs I do - narrower at the bottom, and the wall thicknesses I leave - 3/4 to 1" , I feel perfectly confident leaving them at 75-85% RH initially. This brings them through the magic 20% point where mildew can't maintain itself fairly quickly, especially if I spin and throw unbound water before dismounting, blast with compressed air, or both. Couple weeks tops. Then on the shelf for the final cure to EMC.
Only answer for the black is to bleach.
First, get a hygrometer or two and find out what your relative humidity runs in places where you might store your roughs. Second, take a look at chapter 3 here http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm to find out what that RH translates to in MC. For the type of roughs I do - narrower at the bottom, and the wall thicknesses I leave - 3/4 to 1" , I feel perfectly confident leaving them at 75-85% RH initially. This brings them through the magic 20% point where mildew can't maintain itself fairly quickly, especially if I spin and throw unbound water before dismounting, blast with compressed air, or both. Couple weeks tops. Then on the shelf for the final cure to EMC.
Only answer for the black is to bleach.
Give alcohol soaking a try.....
Hi John:
One of the secondary benefits of alcohol soaking is that it kills most things that are living in or on the wood - fungi included. Running your roughed-out blanks through an alcohol bath would result in killing most active fungal growth within the wood, as well as those fungi on the surface. In some cases, I think this is even more important than the intended purpose of aiding water loss and reducing drying times. Given the situation and turning style/times you describe, I would predict that soaking your roughed-out pieces in alcohol, and then storing them "loosely" in paper bags (which can he opened periodically), storing them in cardboard boxes (like John Jordan does) , or wrapping them in kraft paper/paper-bag material would be a viable method to use (or at least try) to eliminate the problem you describe. I tried the "surround in shavings" slow-drying method years ago, and after my first few 'scummy black bowl' results, that method was quickly abandoned. I now routinely run most of my wet rough-outs through an alcohol soak. Even if it helps by removing some water, it does provide a good method of reducing or eliminating mold growth on the wood. BTW - I also spin/blow out as much water as I can while the piece is still on the lathe.
I've only done a little wood bleaching (I didn't like doing it or the results!), and I doubt that you would be able to selectively bleach the areas stained with the mildew to make it look "normal". You can either chalk up these pieces as a total loss, or try some other form of surface embellishment to mask the stains. Perhaps woodburning a design or texture might help, or scorching the entire piece, and then sanding back to some "good" wood might produce an interesting result. "Extreme" methods of ebonizing, painting, or gilding would also mask the stains. Just like a bad catch, the mildew stains might be viewed as "another design opportunity"....
Good luck!
Rob Wallace
Hi John:
One of the secondary benefits of alcohol soaking is that it kills most things that are living in or on the wood - fungi included. Running your roughed-out blanks through an alcohol bath would result in killing most active fungal growth within the wood, as well as those fungi on the surface. In some cases, I think this is even more important than the intended purpose of aiding water loss and reducing drying times. Given the situation and turning style/times you describe, I would predict that soaking your roughed-out pieces in alcohol, and then storing them "loosely" in paper bags (which can he opened periodically), storing them in cardboard boxes (like John Jordan does) , or wrapping them in kraft paper/paper-bag material would be a viable method to use (or at least try) to eliminate the problem you describe. I tried the "surround in shavings" slow-drying method years ago, and after my first few 'scummy black bowl' results, that method was quickly abandoned. I now routinely run most of my wet rough-outs through an alcohol soak. Even if it helps by removing some water, it does provide a good method of reducing or eliminating mold growth on the wood. BTW - I also spin/blow out as much water as I can while the piece is still on the lathe.
I've only done a little wood bleaching (I didn't like doing it or the results!), and I doubt that you would be able to selectively bleach the areas stained with the mildew to make it look "normal". You can either chalk up these pieces as a total loss, or try some other form of surface embellishment to mask the stains. Perhaps woodburning a design or texture might help, or scorching the entire piece, and then sanding back to some "good" wood might produce an interesting result. "Extreme" methods of ebonizing, painting, or gilding would also mask the stains. Just like a bad catch, the mildew stains might be viewed as "another design opportunity"....
Good luck!
Rob Wallace
John, you're in a fairly dry area. When I lived in Arizona, I would double brown bag turnings after roughing green and never had a spalting, mold problem that way. They dry in a couple of months without cracking 99.9% of the time. You can get the bags in bulk at shipping supply centers/warehouses.
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I am curious as to whether you have spalting or just blue stain (looks grey). The alcohol soak is good advice. I have found that holly turned in the summer does not stain if soaked in denatured alcohol. This is saying a lot as Virginia in the summer is usually very hot and humid. Some wood will stain overnight.
I also use the alcohol to even out the drying and to stop any spalting. I put it on with a brush the first day and re-apply once after a few days. I have been pleased with the results so far.
Thanks for all the great replies. The species experiencing this problem is red oak and sumac. I suspect putting a bunch of bowls together in a box just creates too much moisture. The suggested bag method may be worth a try. What I am experiencing is grey staining (blue as Barbara indicates). Is this not the start of spalting or something entirely different? I have tried applying oxalic acid bleach to the pieces before storage but his did not seem to make a difference. I will try the alcohol approach as Rob and others have suggested. Should I use denatured alcohol over isopropal (rubbing)? Does it make a difference? I have tried simple wood bleaching in the past but this only lightens the stain at best, but i have only brushed it on, not soaked it. I understand there are different forms of bleaching but I only have tried oxalic acid. Has anyone tried peroxide ("two-step") or chlorine bleaching?
What is unfortunate is that the stain goes completely through the wood so it cannot be turned away. I am with you, Rob, on finding ways to incorporate the stain into the piece. As we say in the ceramics world, "If you cannot fix it, feature it." I cannot bring my self to just toss out a perfectly sound piece, especially if it is a rare wood that I may never see again. Thank you all again for some very good inputs......John
What is unfortunate is that the stain goes completely through the wood so it cannot be turned away. I am with you, Rob, on finding ways to incorporate the stain into the piece. As we say in the ceramics world, "If you cannot fix it, feature it." I cannot bring my self to just toss out a perfectly sound piece, especially if it is a rare wood that I may never see again. Thank you all again for some very good inputs......John
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Gray/black spots are mildew. Bluestain in the sapwood - especially of conifers - is not the same thing. Nor is spalt, which takes a lot of time to develop. http://www.fpl.fs.fed.us/documnts/techline/blue-stain.pdf
Your suspicions are correct, though they may prove less correct in the summertime than the winter. In the summer at Beale I boxed, and threw away the wet boxes after the first few days to re-box. I also used a cabinet with ventilation, which took less effort, and thus became my preferred method of maintaining an area of high humidity in the dry heat.
Alcohols or Ketones - and it must be one with a lower boiling point than water - might flash the surface and get it below the 20% MC, but if you confine thick pieces closely in bulk you'll probably build back up over it, and risk mildew again. If you've flashed -case-hardened -the surface, you want to preserve the benefit of your expense and effort by loose moisture control techniques afterward. Bagging or wrapping to cut down on circulating air is probably going to be enough until summer.
Best advice is still not to follow a fixed recipe or magic one size fits all plan, but to use instruments to discover where you are and how you're progressing. Great thing about science is repeatability. Since it's Relative Humidity - the ability of the air to carry water - that counts, as years of kilning have proven, you can control it, and leave chance out of the equation.
Just a thought if your using the same box and just changing the pieces in it once there is mold or mildew in the box your spreading it to whatever you add to the box.
You can also try holding a air nozzle up against the wood and blowing all the free water out of the wood before you set the bowl back to dry. It will prevent a lot of problems with spalting or the wood loosing it's color. John Jordan shows this in his demo's. If it helps him produce the beautiful work he does then it should help anyone.
Jack`
Jack`