Specific Gravity of Dawn Redwood

      We're talking about a particular tree species here, but the comments on determining specific gravity apply to any wood sample. April 27, 2007

Question
Anybody know the specific gravity for dawn redwood (Metasequoia)? The tree has a very interesting history. How can I do a test to find out the specific gravity of this wood without having my oven running for two + days while I'm at work?

Forum Responses
(Sawing and Drying Forum)
From contributor G:
Eureka! I believe if you take a pail and measure the volume of it filled to the brim in liters, you can then place a block of your wood, which you have previously weighed in kg (the mass), into the pail, catching the overflow in a tub. The displaced volume is the volume of your chunk and then Density = Mass / Volume.



From contributor J:
Hoadley's book on identifying wood has an easy test for SG.


From Professor Gene Wengert, forum technical advisor:
Right here at WOODWEB you can find "Drying Hardwood Lumber." Go to page 9 of the text.

Drying Hardwood Lumber



From contributor K:
I would like to understand this better. If the wood is green, won't that throw the equation off? It seems to me that he will still need to dry X amount, to measure the dry floating weight first, then completely immerse it to find the other volume. I think I would even weigh it after to see how much soaked in even from a quick immersing.


From contributor R:
SG does vary a little between wet and dry, but remember that when wet, the weight is thrown off because of water, but the volume is also greater... due to lack of shrinkage. You mentioned weighing to see how much water soaked when testing SG dry. In lab conditions (actually you could also do it at home), the dry sample pieces are dipped in molten wax to seal, so they won't pick up water when submerged. This wax coating is so thin, the added weight is generally ignored.


From Professor Gene Wengert, forum technical advisor:
We measure specific gravity in two main ways... oven dry weight and green volume - oven-dry weight and 12% MC volume. It is kind of funky… The difference between the two values is the shrinkage of the wood as it dries. That is, in drying, the density increases 6% to 15%, give or take, depending on species. Note that because SG is measuring the density with respect to water, the amount of water is not a factor, per se.

I found a green SG of 0.27 in the literature.



From contributor J:
I believe that Wagner uses SG at 12% volume for their meters, not OD volume. Someone correct me if I'm wrong.

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