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Mildew growing in sapwood in 20 minutes??

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Yesterday I was turning a live edge piece of walnut with the bark on, and what looked like mildew grew in the sapwood at an astonishing pace. As I hollowed the interior a few of the small brown spots in the white sapwood began to look more prominent. About 20 minutes into this I noticed green spreading across the end grain on the outside (and eventually the inside) of the sapwood. I completed the turning, this will be a once turned bowl, and put it in a paper bag while I did a little research. The tree was felled a month or so ago, cut into short lengths and Anchorseal applied to the ends. There was a little mildew visible when I prepped this log into two round blanks yesterday. The first one went onto the lathe within the hour.

I didn't find any consensus about what's going on, the two main opinions being 1) mildew can grow that quickly if it's already deep in the wood and is exposed to oxygen, or 2) it's not mildew at all, but "tannins" from the heartwood bleeding into the sapwood. Not being sure, I spritzed the bowl inside and out with diluted bleach to kill whatever might be growing. I hope it's superficial and will sand out. The bowl is back in a bag for a few days before I sand and remove the tenon.

Any ideas? Thoughts? Is this something common that I've missed so far? Thanks in advance, I'm really hoping to get rid of the dingy look if possible. Photos show the wood while turning and then later when sprayed with bleach. Thank you for any info.
 

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Joined
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Black walnut, it is hard to keep the sapwood white, The heartwood color will leach into the sapwood (as well as bark dust) , but I have never seen that greenish color come out in any wood I have turned wet or dry, unless it is "juice" from the cambium layer that is being forced into the sapwood from dull tools/ scrapers is all I could think of. Your last photo (when bleached), though looks pretty normal to me for walnut after it has oxidized a bit from being wet turned. You may find after you let the bowl dry completely, and sanded, that the blotchy appearance may gradually reduce, but once you apply a finish to it, the sapwood will surely darken.
 
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Thanks Brian, the idea of something leeching into the sapwood from the cambium rather than the heartwood hadn't occurred to me. I don't think it's about dull tools, I enjoy turning much more when I keep them super sharp and I went to the grinder at least a couple times during this bowl. I have turned a fair bit of walnut and haven't seen any of the oxidation you're mentioning, but I usually turn away most of the sapwood. Can you tell me a little more about that - what it means and if it can be avoided somehow?
 
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Not Mildew, but wood sap reacting with the oxygen in the air.
Thanks Leo. Is this something that can be avoided (not the air of course, but the discoloration)? Do you find it sands away from a dry piece? I'm also wondering if felling the tree later in the Fall/Winter when the tree is inactive would mean less of this.
 
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In September 2022 I went down to the Minneapolis St. Paul Metro Area and helped take down a live walnut that was about 24" diameter on the butt end from my sisters yard then hauled the majority of the tree back to my home in the MN lakes area. The main trunk was about 7' long so I milled it into timbers with my Woodmizer band mill, but that still left enough pieces for turning. In December I turned this goblet form as a once turned item from small pieces that had been stored outside in the cold and the sapwood stayed quit white.
22071Goblet1.JPG
In January of 2023 I turned this from a piece that had been stored inside my heated shop so some of the sap wood had started to turn brown except for one area.
23002Goblet.JPG
As far as the green stain I have never seen that before and I have done a lot of walnut turnings.
 
Joined
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Thanks Brian, the idea of something leeching into the sapwood from the cambium rather than the heartwood hadn't occurred to me. I don't think it's about dull tools, I enjoy turning much more when I keep them super sharp and I went to the grinder at least a couple times during this bowl. I have turned a fair bit of walnut and haven't seen any of the oxidation you're mentioning, but I usually turn away most of the sapwood. Can you tell me a little more about that - what it means and if it can be avoided somehow?
Oxidation I am referring to is when the sapwood goes from milky white to a slightly darker brown-ish (yellowish leaning) color , but still on the white side of the spectrum.. - I have no more truly wet walnut (most of what I have left is now seasoned sitting out under a tarp), or I'd go cut a chunk and take a few photos to compare to... The little brown splotches and "dots" seem to come out at will as the wood dries further but I have seen that in every walnut piece I have turned. the whiteness does not stay fully milky white - it does darken as it experiences exposure to air/finish/sunlight and as far as the leeching of colors, it is fairly common for the production mills to steam their walnut to get the dark chocolate brown color to spread through the sapwood from the heartwood - You can also get the sapwood stained from sanding the bowl while on the lathe if you overlap from bark or heartwood into the sapwood, but in my own experience, I hadn't had that problem once I was able to get nice clean cuts that required almost no sanding, and just let the bowl dry completely before finishing.

As Don posted above - Seems to me most of the walnut comes out better if allowed to season a little bit , even by a few days, rather than turning it when it is sopping wet..
 
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As Don posted above - Seems to me most of the walnut comes out better if allowed to season a little bit , even by a few days, rather than turning it when it is sopping wet..
I didn't intend to say that seasoning helps, the first picture of the goblet form with the creamy white sapwood did not really start to dry at all and as I turned it there was a lot of water/sap flying off. I think the key to keeping the light color is to turn it once very thin ( that one was around 1/16" or 1.6mm thick) and it seems to dry rapidly enough (that one was dry in about 2 days time) to prevent that color change that normally happens when the inner most sapwood transitions to heart wood.
 
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Brian blowing all the sap out/off the wood will lessen the color leaching, I never really tried that successfully, what I did try is turning a shallow bowl from just the white sapwood, so there isn't basically any sap to migrate and then oxidize.
This is that bowl and it stayed pretty white but over time even that color changed to a darker color, so to me it isn't worth the effort, I like the Walnut showing the light and dark wood, and removing most sap will give you a nicer outcome IMO .
Black Walnut sapwood.jpg

And this is the same bowl several years later.

The white color does change.jpg

Love this, but even that will change.

Black Walnut crotch.jpg
 
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Joined
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I didn't intend to say that seasoning helps, the first picture of the goblet form with the creamy white sapwood did not really start to dry at all and as I turned it there was a lot of water/sap flying off. I think the key to keeping the light color is to turn it once very thin ( that one was around 1/16" or 1.6mm thick) and it seems to dry rapidly enough (that one was dry in about 2 days time) to prevent that color change that normally happens when the inner most sapwood transitions to heart wood.
Yeah, Seasoning may not have been the most appropriate term, but to me, a couple months' worth of sitting (September to December) is still a bit "seasoned" which is where that came from- It was my term for it sitting around for a while after a living tree has been cut down. - Likewise, as to Leo's comment blowing out the sap can keep it fairly white but even then, it's still going to darken/oxidize/age - whatever term one wants to use, it doesn't STAY pure milky white (Though it doesn't start to turn black/purple heartwood-y color without an y heartwood to leach color across.) Even your thin-walled goblet shows some darkening of the sapwood, it isn't what I'd call pure white any more... Just shows the variety that is Black Walnut...

Basically I'm saying I agree with what you and Leo have already been saying, but for lack of better defined terminology, we may be mis-understanding each other. (as Leo had already said some of the discoloration due to the sap/sapwood "reacting to oxygen in the air" - In other words, Oxidizing.. so Trees/Logs left sitting out for even a couple months, are still "a bit" seasoned)
 
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In September 2022 I went down to the Minneapolis St. Paul Metro Area and helped take down a live walnut that was about 24" diameter on the butt end from my sisters yard then hauled the majority of the tree back to my home in the MN lakes area. The main trunk was about 7' long so I milled it into timbers with my Woodmizer band mill, but that still left enough pieces for turning. In December I turned this goblet form as a once turned item from small pieces that had been stored outside in the cold and the sapwood stayed quit white.
View attachment 57547
In January of 2023 I turned this from a piece that had been stored inside my heated shop so some of the sap wood had started to turn brown except for one area.
View attachment 57548
As far as the green stain I have never seen that before and I have done a lot of walnut turnings.
First of all, gorgeous work Don, and great information with regard to the timing of your work on these two pieces. Interestingly, the overall darkness that spread to the sapwood in the second piece left the spots visible in the patch of remaining white. Those spots are what began to intensify before my eyes the other day. Thank you so much for the input.
 
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Brian blowing all the sap out/off the wood will lessen the color leaching, I never really tried that successfully, what I did try is turning a shallow bowl from just the white sapwood, so there isn't basically any sap to migrate and then oxidize.
This is that bowl and it stayed pretty white but over time even that color changed to a darker color, so to me it isn't worth the effort, I like the Walnut showing the light and dark wood, and removing most sap will give you a nicer outcome IMO .
View attachment 57549

And this is the same bowl several years later.

View attachment 57550

Love this, but even that will change.

View attachment 57551
These are beautiful Leo, thank you for sharing them. Nice to see some clear evidence of darkening I can expect with walnut where I leave sapwood in place.
 
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I appreciate all the good information here. Seems like the evidence shows the sapwood on walnut is likely to darken with time. It also seems like the green color that spread across my bowl is at least somewhat unusual and so far undefined. Perhaps it's something local growing inside the tree and reacting to the air, whether that's fungus, mildew or staining from other parts of the piece. I'm still hoping at least that green will sand out, and I'll post more here if I learn anything further. Thanks again!
 
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My first thought was that you were getting iron dust on your walnut, and those spots appear almost instantly. Not the case here... As others say, it is difficult to keep the sap wood white.

robo hippy
 
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My first thought was that you were getting iron dust on your walnut, and those spots appear almost instantly. Not the case here... As others say, it is difficult to keep the sap wood white.

robo hippy
Thanks Robo, I agree it's not likely iron dust. And I'm glad to understand more now about walnut sapwood darkening, in both short and long term. I'm counting on that to disguise some of the dark spots that materialized while still on the lathe. Cheers!
 
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