Replies

1. 
   clampman2 | Mar 18, 2003 07:20am | #1

   I'm almost certain they are referring to the method of kiln drying that was used. Many big kilns use steam during the kiln drying process to speed it up without associated checking, warping, case hardening etc.

   Others use dehumidifying kilns. Some woods, cherry in particular, look much better to me if they are dried in a dehumidifying kiln. Steam kilns cause the colors in cherry to bleed, and the grain is much duller looking because of it.

   Clampman

2. 
   forestgirl | Mar 18, 2003 07:43am | #2

   I asked about this a little while back.  The last time I was Edensaw in Port Townsend, I asked the owner.  He said some woods are steamed to even out the color.  He was pretty busy, so didn't have time to ask him about details, but the next time I'll try to get some more info.

   forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

1. 
   jjf | Mar 18, 2003 03:47pm | #3

   Before the wood is dried or veneer is peeled it is put in a steam chamber, a large wooden box mafe fromm timebrs, and steam is pumped into it.  This is done almost always for walnut and some other speices also.  The chemical that give walnut it's color are water soluable and will migrate from the heartwood to the sapwood wahen it is expsoed to hight emperatures and moisture.  This will darken the sapwood while lightening the heartwood.  This results in more "dark" lumber the sawyer can sell.  In some woods steam is used to treat the lumber to increase the permeability.  Permeability is a measure of how easy it is for water to move through the wood.  When treated for this they can dry the wood a little faster with our cracking.

1. 
   forestgirl | Mar 18, 2003 07:33pm | #4

   Thank you Jim!  I guess you weren't around last year when I posed this question.  I'll bookmark your post for future reference.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

1. 
   jonsherryl | Mar 19, 2003 12:45am | #5

   Forestgirl, Jim's conclusions won't lead you astray, but the chemistry involved in steaming walnut works a little differently than described. The steam doesn't cause the pigment to migrate from the heartwood to the sapwood so much as it causes the hydro juglone in the sapwood to polymerize into dark pigments. This was demonstrated in tests conducted back in the late 1960's, when it was discovered that a kiln charge of walnut sapwood could be caused to darked, even though no walnut heartwood was present. Further tests revealed it is mostly the heat that causes the conversion and the conversion is most efficient at temperatures slightly above the boiling point of water (around 230 degrees F.) The moisture in the steam seems to assist in the conversion by conveying the heat...in that they also discovered that air dried sapwood could be made to darken when exposed to heat, but it was found that moist, "green" sapwood converted much more quickly.

   What causes steam treated walnut to look a little dull and lifeless is that the steaming process destroys the heartwood's highlights and tends to remove any remaining variegation in the wood, probably by completing the conversion of available juglone. Although the research didn't address it specifically, I suspect steaming also tends to leach out some of the pigments from the wood in total. In any event (in my experience) it seems that even the heartwood of walnut that has been steamed takes on a slightly lighter and more grayish hue. It's never as nice as air dried stock, with its beautiful purple highlights...Unfortunately, over time, even the air dried stock loses these highlights.

   As to the point about pre-steaming wood to shorten the kiln time and reduce degrade, that seems to be true...and it's used to process some species that tend to distort or check badly when kiln dried without the benefit of pre-steaming. It isn't worth the added processing costs when drying the more stable species, though. Pre-steaming is usually done to affect the wood's pigmentation and make more of the log usable as top quality cabinet wood. Walnut and cherry are the two species where it seems to be the most profitable way to go.

   Edited 3/18/2003 5:49:32 PM ET by Jon Arno

   Edited 3/18/2003 5:50:50 PM ET by Jon Arno

1. 
   clampman2 | Mar 19, 2003 07:07am | #6

   Thank you Jon,

   Hope you are still here. I have a question for you, if I can do the computereze and get the picture to show up. Do you know what causes these burl-like warts so common on cherry? And the figure as well?View ImageI still don't like cherry that has been steamed.

   Thanks,

   Clampman

2. 
   SgianDubh | Mar 19, 2003 07:25am | #7

   Sorry, clampman, not Jon here, but I'll offer an opinion anyway just for the hell of it. The warts look like a small group of wee branches that got lopped off or encased before they could grow much beyond the twig stage.

   The figure-- that wavy look? Looks like where the grain near the surface is not quite straight and waves up and down into and out of the surface. Slainte.Website    The poster formerly known as Sgian Dubh.

3. 
   jonsherryl | Mar 19, 2003 01:00pm | #9

   Clampman, from what I can gather from the photo (as usual, not much) what it shows appears to be anatomical and RJ's thought that it might be a bud cluster, could be right on the mark. Cherry is also susceptible to insect damage and it's method of healing the wounds is to patch them up with a gum that turns black in color over time. Sometimes this "gummy" figure looks a little spotty, like bird's-eye, but I don't think this is what your picture shows. It looks more like a bulge or bump in the grain that has yielded sort of a concentric circle pattern on the surface of the milled wood.

4. 
   clampman2 | Mar 25, 2003 08:03am | #12

   thank yous to Jon and RJ. I finally took my loupe to the other shop and looked closely at the warts, which consist of a bunch of dark, roughly circular spots with holes in the centers surrounded my grain going every which way.

   I assume they are as RJ suggessted.

   Tahnks again

   Clampman

5. 
   forestgirl | Mar 19, 2003 07:56am | #8

   Thanks Jon, another mystery solved!!  One question, obviously from a novice:  Where you say "Unfortunately, over time, even the air dried stock loses these highlights" -- this doesn't take place if the piece is finished before it gets to this point, does it?  I've read about cherry darkening as it ages under a finish, but does this loss of highlights in walnut take place only when it's unfinished?forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

6. 
   jonsherryl | Mar 19, 2003 01:25pm | #10

   Bad news, Forestgirl...those beautiful magenta-purple highlights in air dried walnut are fugitive and, finished or unfinished, they eventually go away. I suspect these purplish pigments are mostly light sensitive...meaning they break down after long exposure to light...as opposed to being destroyed by oxidation.

   I haven't seen any research on this subject, but the reason I think the highlights are probably light sensitive is that I recently planed some beautiful air dried walnut that I bought over 40 years ago. The fresh surface still displayed fantastic purple highlights. If these pigments were sensitive to oxidation, I suspect they would have given up the ghost years ago...since air has had plenty of time to infiltrate the wood to a depth well beyond the amount of wood tissue I removed in the planing process...But who knows?...the chemistry of wood pigments gets pretty complex and there very likely could be multiple (sequential reactions) that eventually cause these color changes.

7. 
   jjf | Mar 20, 2003 04:12pm | #11

   Sounds like Jon's source of information is more solid than mind.