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Thread: Have experience with finishing cottonwood? Dry spots are forming on my bow!?!

  1. #1
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    Question Have experience with finishing cottonwood? Dry spots are forming on my bow!?!

    This question is for those of you whom have experience in finishing cottonwood bowls. I am really hoping you, my beloved members of this forum, can help me with finishing on a big cottonwood bowl that I recently turned. Basically, I turned a whopping 20" cottonwood bowl that came out well. I sanded it up to a very fine grit--couldn't get it real shiny, but got it nice and smooth. Then, I applied a liberal amount of raw linseed oil to it. Here it was after that:

    15 Overall Angle 1.jpg16 Overall Angle 2.jpg

    Now, for the problem that I need your help with... Give it a day or even less, and dry spots started to form on the outside, as if the oil is disappearing:

    Dry Spot.jpg

    How do I retain that finished, oiled look?

    I've never worked with cottonwood, and I've never had this happen with any other wood that I have worked with. I didn't apply wax to it. Would it help if I were to apply wax after the oil? I'm just hesitant that since this is happening, the oil could still saturate into the wood, leaving the dry spots, but now with wax on the outside, making it even more difficult for me to apply oil in the future if need be. I'm thinking if I am left with wax only, those spots will lack the deeper tones that the oil gave the wood. My guess as to why this is happening is that the oil eventually saturates so deeply into the wood that it escapes the visible surface in these particular areas. So, one unattractive solution, it seems, is that I could reapply the oil whenever the spots appear, over and over until they quit forming (if that ever happens), but I'm hoping there is a better solution than that. I'm not confident that in doing that, the dry spots wouldn't form in the future. So, I'm enlisting those of you whom have experience in finishing cottonwood...

    This bowl means a lot to me. In honor of Father's Day, I turned a bowl so big that my 7 month old could fit into it, and one day I will tell her that when I made it, she could fit inside of it. So, I hope it becomes special to her, and I want to finish it optimally. For this, I thank you sincerely for your help.
    Last edited by Chris Gunsolley; 06-23-2016 at 1:00 PM.

  2. #2
    Multiple coats as the wood is simply soaking up the oil. But, I would suggest BLO (boiled linseed oil) instead of raw - if that is your desired finish. The BLO will cure out slowly, but a lot faster than the raw stuff. The raking light in the pic seems to reveal tool marks, but that could be an illusion. You might consider wet sanding with BLO to really get a nice finish.

  3. #3
    It is surprising that the oil has absorbed to the point of disappearing on the surface. It is also odd that it's discolored in such a blotchy manner. Something looks off to me as if something else is happening. Have you put anything else on the wood during your sanding? Was this turned green? What grit did you sand up to?


    I would resand the entire bowl. Not to get all the oil off, but to reduce the tool marks as John points out. If this was turned green, I'd let it dry properly (which could mean several weeks depending on your wall thickness) and then resand at the highest grit.

    After you get it to 400 or 600 grit (you can wetsand with mineral spirits after 220 if you wish).

    Once sanded, I would mix equal parts BLO, mineral spirits and polyurethane and repeatedly apply, let soak for a minute, then buff off. This will give you all of the look of the pure oil finish with more durability.

    Even if you are able to burnish up the raw linseed oil and even up the coverage; it will only be temporary. Eventually, the bowl will become dull and you'll have to refresh the surface. If you use an oil/varnish, the frequency of that required refresh will decrease.

  4. #4
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    Using BLO or Walnut oil, I've seen it soak in and even dull quite a bit, but I've never seen it soak in to the point it appeared to... well... disappear. I've never worked with Cottonwood, either; maybe it's deserving of the name! It almost looks like that section of the wood has something in it that's repelling the oil (and quite effectively!)

    Prashun's plan sounds interesting, but I think I'd hold off on applying any kind of film finish until I knew what was going on. I could imagine ending up with that discoloration underneath a layer of poly that I'd just have to sand off again.

  5. #5
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    Raw linseed oil usage is a mystery to me. Tung oil/mineral spirits or Watco ect. are faster, easier and much harder finish the any raw oil. Noticed all the "dry spots are in the endgrain.

  6. #6
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    Chris Poplar is a soft wood with lots of room within the fibers of that wood, it can contain lots of water or lots of oil.

    I don’t know why you would use raw linseed oil though, it wont harden up for eternity, I made that mistake to use it on a picnic table I build some 50 years ago , it turned all black and stunk, as the oil got rancid and fungus got into it, as I was told it was a good oil for outside use .

    I have turned a few pieces of Poplar, but I turned them mostly thin walled and then used PTO (Polymerized Tung Oil), not to get a shiny finish though, just a more low gloss that I like on something like that.

    I will always just get enough oil to cover the wood, let stand for about 10 minutes en than wipe the bowl dry, set the bowl in a warm dry place and let the oil harden, takes a good night or usually a day for me before adding another coat, and repeat this as the first one, depending the gloss you want, you might need just two or maybe 4 or 5 for high gloss.

    If you want to polish it, wait at least a week and better longer than that to get a harder finish that will give you also a higher gloss.

    When spalted Poplar can look good, plain it is a rather boring wood, turned very thin it will show the light through it.

    Poplar crotch.jpg Poplar bowl.jpg thinwall.jpg Wormy Poplar.jpg

    This one has a thicker wall as the wood was already too soft for a clean cut, even a skew was barely able to make the outside smooth, and the inside was harder to do of course no skew but a spindle gouge was giving me the best cut, and still had a bit of roughness in the bottom.

    Mind you I would NOT recommend using a skew or spindle gouge on a bowl ever, this is the do as I say, not as I do.
    Spalted Poplar.jpg
    Last edited by Leo Van Der Loo; 06-24-2016 at 1:24 AM.
    Have fun and take care

  7. #7
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    Due to a problem with my recess, I was actually lucky to walk away from this one with any bowl. After I started hollowing it out, one of the walls on my recess started to give in at a point at which it makes contact with one of the jaws. (I think I didn't make the recess deep enough.) This created major runout, so I had to turn and sand the entire thing no faster than about 400 rpm. (Yes, that took a long time.) I tried to keep the tool marks to a minimum with the runout, and what you see in the picture is what I ended up with. I reached a point at which I had to accept the bowl as it is. I suppose I'll designate it a user and replace all three of my fruit bowls with this one I don't think the marks are too bad for a utility bowl I am to use myself, as opposed to selling. I'm a little bummed about not being able to finish it perfectly, but I like its shape, it's structurally sound and it'll do one heck of a job at being a bowl...

    My research tells me that the optimal method for getting a smooth surface with cottonwood would be to turn it at a fast speed and use a shear cutting technique using scrapers as opposed to bowl gouges. I realized this and prepared mentally before turning this bowl. The problem was that because of the runout, I couldn't turn it fast, so I couldn't get a very sharp cut, and the runout also encouraged the tool marks as it hit one side deeper than the other.

    So, where I'm at with this bowl right now is that I don't think there's a way I can remount it, as the recess is weak and they don't make cole jaws large enough to accommodate a 20" bowl. If I could mount it on the cole jaws, I could cut a new recess, re-shape the bottom a bit, touch everything up and sand at the faster speed that I should have been turning at the first time around. But, unfortunately, I don't think that's an option. I thought about gluing a cylinder in the recess that fills the whole thing, then gripping it with my tower jaws to spin the bowl, but then I wouldn't be able to remove it, again, because I wouldn't have cole jaws to remove it safely.

    All in all, I don't think I can remount this bowl. Let me know if you have any ideas for doing that, or for refinishing this bowl without mounting it. The only viable solution I can think of right now is that I could sand it with a rotary sander, then re-finish it with something other than raw linseed oil.
    Last edited by Chris Gunsolley; 06-24-2016 at 3:30 PM.

  8. #8
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    Quote Originally Posted by Leo Van Der Loo View Post
    Chris Poplar is a soft wood with lots of room within the fibers of that wood, it can contain lots of water or lots of oil.

    I don’t know why you would use raw linseed oil though, it wont harden up for eternity, I made that mistake to use it on a picnic table I build some 50 years ago , it turned all black and stunk, as the oil got rancid and fungus got into it, as I was told it was a good oil for outside use .

    I have turned a few pieces of Poplar, but I turned them mostly thin walled and then used PTO (Polymerized Tung Oil), not to get a shiny finish though, just a more low gloss that I like on something like that.

    I will always just get enough oil to cover the wood, let stand for about 10 minutes en than wipe the bowl dry, set the bowl in a warm dry place and let the oil harden, takes a good night or usually a day for me before adding another coat, and repeat this as the first one, depending the gloss you want, you might need just two or maybe 4 or 5 for high gloss.

    If you want to polish it, wait at least a week and better longer than that to get a harder finish that will give you also a higher gloss.

    When spalted Poplar can look good, plain it is a rather boring wood, turned very thin it will show the light through it.

    Poplar crotch.jpg Poplar bowl.jpg thinwall.jpg Wormy Poplar.jpg

    This one has a thicker wall as the wood was already too soft for a clean cut, even a skew was barely able to make the outside smooth, and the inside was harder to do of course no skew but a spindle gouge was giving me the best cut, and still had a bit of roughness in the bottom.

    Mind you I would NOT recommend using a skew or spindle gouge on a bowl ever, this is the do as I say, not as I do.
    Spalted Poplar.jpg
    Leo,

    Your report on the picnic table scares me, and I've decided against using raw linseed oil as finish on bowls. I'll have to re-mount, re-sand, and re-finish the 4 bowls that I finished with it. The reason I chose raw linseed oil is that I like the effect the linseed oil has on wood, but I wanted the finish to be food safe. Boiled linseed oil is not food safe, but raw linseed oil is. I was willing to stick it out for a month and let the oil dry. Considering that it goes rancid, and what you said about the picnic table, I wish I could extract it from those 4 bowls now. I'll do what I can, which is re-sanding and re-finishing.

  9. #9
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    Quote Originally Posted by Chris Gunsolley View Post
    Leo,

    Your report on the picnic table scares me, and I've decided against using raw linseed oil as finish on bowls. I'll have to re-mount, re-sand, and re-finish the 4 bowls that I finished with it. The reason I chose raw linseed oil is that I like the effect the linseed oil has on wood, but I wanted the finish to be food safe. Boiled linseed oil is not food safe, but raw linseed oil is. I was willing to stick it out for a month and let the oil dry. Considering that it goes rancid, and what you said about the picnic table, I wish I could extract it from those 4 bowls now. I'll do what I can, which is re-sanding and re-finishing.
    If you really like the effect of BLO, but want it foodsafe, look up TY Fine Furniture's food grade utility finish. It's a mixture of polymerized linseed oil and something else that I can't recall right off the top of my head. It's supposed to be safe enough to drink out of the bottle (not that you'd want to). It was introduced to my turning club (Palmetto Woodturners) by Mike Sorge, and I got a small bottle to try. It dries almost as fast as BLO and smells wonderful.

  10. #10
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    Quote Originally Posted by Aaron Craven View Post
    If you really like the effect of BLO, but want it foodsafe, look up TY Fine Furniture's food grade utility finish. It's a mixture of polymerized linseed oil and something else that I can't recall right off the top of my head. It's supposed to be safe enough to drink out of the bottle (not that you'd want to). It was introduced to my turning club (Palmetto Woodturners) by Mike Sorge, and I got a small bottle to try. It dries almost as fast as BLO and smells wonderful.
    Wow, sounds great, Aaron! I'll definitely give it a shot. Thanks for mentioning it!

  11. #11
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    Quote Originally Posted by Chris Gunsolley View Post
    Wow, sounds great, Aaron! I'll definitely give it a shot. Thanks for mentioning it!
    No problem. I just went to check my bottle. It's made of "organic polymerized flax seed & organic shea nut oil" (flax seed oil, of course being the same thing as linseed oil). The bottle says it generally dries in 1-2 hours, but I find that to be heavily dependent on the type of wood. I like it for soft maple because it dries much faster than another favorite (Mahoney's utility finish, which is Walnut oil). The walnut oil can take up to a week to dry in my attic (probably about 120F). The TY oil takes about half that time (though I usually leave it for a week anyway).

  12. #12
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    Quote Originally Posted by Chris Gunsolley View Post
    Wow, sounds great, Aaron! I'll definitely give it a shot. Thanks for mentioning it!
    Just one for heads up, shea nut.jpg
    Have fun and take care

  13. #13
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    Quote Originally Posted by Chris Gunsolley View Post
    Due to a problem with my recess, I was actually lucky to walk away from this one with any bowl. After I started hollowing it out, one of the walls on my recess started to give in at a point at which it makes contact with one of the jaws. (I think I didn't make the recess deep enough.) This created major runout, so I had to turn and sand the entire thing no faster than about 400 rpm. (Yes, that took a long time.) I tried to keep the tool marks to a minimum with the runout, and what you see in the picture is what I ended up with. I reached a point at which I had to accept the bowl as it is. I suppose I'll designate it a user and replace all three of my fruit bowls with this one I don't think the marks are too bad for a utility bowl I am to use myself, as opposed to selling. I'm a little bummed about not being able to finish it perfectly, but I like its shape, it's structurally sound and it'll do one heck of a job at being a bowl...

    My research tells me that the optimal method for getting a smooth surface with cottonwood would be to turn it at a fast speed and use a shear cutting technique using scrapers as opposed to bowl gouges. I realized this and prepared mentally before turning this bowl. The problem was that because of the runout, I couldn't turn it fast, so I couldn't get a very sharp cut, and the runout also encouraged the tool marks as it hit one side deeper than the other.

    So, where I'm at with this bowl right now is that I don't think there's a way I can remount it, as the recess is weak and they don't make cole jaws large enough to accommodate a 20" bowl. If I could mount it on the cole jaws, I could cut a new recess, re-shape the bottom a bit, touch everything up and sand at the faster speed that I should have been turning at the first time around. But, unfortunately, I don't think that's an option. I thought about gluing a cylinder in the recess that fills the whole thing, then gripping it with my tower jaws to spin the bowl, but then I wouldn't be able to remove it, again, because I wouldn't have cole jaws to remove it safely.

    All in all, I don't think I can remount this bowl. Let me know if you have any ideas for doing that, or for refinishing this bowl without mounting it. The only viable solution I can think of right now is that I could sand it with a rotary sander, then re-finish it with something other than raw linseed oil.
    Best cutting on soft wood is NOT a scraper, but a cutting tool like a bowl gouge.

    Better sanding technic is a slow rotating piece and power sanding with rotating disks, do not use a coarse grit as it will tear the wood grain and than you have a job fixing that up.
    Have fun and take care

  14. #14
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    Quote Originally Posted by Leo Van Der Loo View Post
    Just one for heads up, shea nut.jpg
    Good point. As with walnut oil, there is at least a potential danger for those allergic to nuts.

  15. #15
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    Take care when mounting very soft and weak woods and adjust your methods to the wood. Expanding dovetails are usually too weak in soft woods--tenons are also suspect especially using green soft woods. Glue blocks and faceplates are much more safe.

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