Question on wood chemistry

[oldpilgrim]

I have 6 grand daughters, ranging from 8 to 22 years old.....all very smart kids.

Today the 14 year old, Emily, asked me a question I couldn't answer. She's in a special honors group in high school. Her classes are set up for just for the super smart and she has an average of about 3-5 kids in each class. (she gets her smarts from me )

She spent Saturday and most of today here and when we were outside walking in the woods in the nice Fall weather, we went over to my several 'holz hauzen' style of fire wood stacks and asked if I was going to burn the wood in the gray piles or the ones in the (newer) brown colored stacks. She knew the answer really but when I confirmed here suspicions, she then asked why does the wood turn gray as it ages.

I couldn't tell her.

So all you knowledgeable wood/chemical experts out there, why does it turn gray as it ages? Make me appear smarter to Emily than I really am.

 

[Clint S]

I would guess it is UV light breaking down the cells. Could also be dirt, mold ,pollen particles adhering to the surface

 

[byronlj]

"The natural weathering process of wood is a combination of chemical, mechanical, biological and light-induced changes, all of which occur simultaneously and affect each other. For instance, as air moves over the surface of a wood deck, dust, pollen, dirt, and air pollutants replace the exposed colored cells of the wood. This slow transformation is also made possible through the exposure of the sun’s ultraviolet rays, or salt particles in coastal areas. Depending on the species of wood, these changes can occur anywhere between a few months to years."
I kind of borrowed that answer from the net,
Dave

 

[oosik]

I have Ponderosa pine almost exclusively here. It will turn blueish-grey after being felled and cut to length. This color will run thru the entire length of the chunk of wood. Many contractor who build the uber expensive custom homes pay a premium price for this wood. The trees are cut to 12' or 14' lengths, left to "cure" and then sliced into "one by" lumber. The blue-grey color is exposed in large streaks down the length of the board. I've alway been told this color is due to a type of mold that grows in the wood when exposed to air. They use these boards as expressive sheathing in specific rooms in the house.

 

[dave1949]

We have "blue stain" in eastern white pine. It's not considered a good thing here.

Blue Stain, Also Called Sap Stain | Summer 2009 | Center for Northern Woodlands Education

 

[oosik]

You are absolutely correct, dave. You will never see this condition on construction grade lumber now. Anyhow, I've only seen P. pine used as really rough cut or this blue-grey lumber and only as decorative paneling. I had four old buildings here - from the 1892 homesteading days - when we moved onto the property. I sold the side boards - 1" x 12" rough cut pine - to a contractor. He used that stuff in the rec room of an expensive custom home. All I know is the blue-grey stuff burned just as well as all the other. About 1 in 5 trees, that I fell for firewood, would develop this weird shading.

It was impossible to tell if the old buildings had any of this shading condition - they were all extremely weathered. I don't think the old homesteader ever bothered to paint anything.

 

[dave1949]

You are right. I hardly ever see blue stain in construction lumber. I had forgotten about the albino strain of fungi that can be used to displace the blue.

Blue stain shows up once in a while in 1x4 strapping, 1x6 T&G, stuff like that. I've never noticed having any problems using it. The T&G pine at our local lumber yard has waxed ends. Mid to darker stains seem to cover it reasonably well.

Seems to be always a good market for old, weathered siding and barn beams.

 

[oldpilgrim]

I've seen the 'blue stain' you mention but I was referring to the general 'graying' that occurs on about every type of wood as they dry out over the course of time, around here, anyway.

example, newly split:

with a few months drying:

and it gets grayer as it gets older. This happens on about every variety of wood I split. It's generally thought of as weathering, I guess, as it happens on pine, cedar shingles, etc. Just about wood left outside unprotected.

Somewhere, I think I remember hearing about 'tannin' having something to do with it.

It's the little things that get me wondering...completely unnecessary to know, but interesting when you do know. Seems like I have a few of you wondering now too.

 

[dodge man]

My turns gray also. Just tell here its little elves running around with spray paint.

 

[oldpilgrim]

My turns gray also. Just tell here its little elves running around with spray paint.

I told her it turned gray when it got old just like people's hair turning gray, but I think she saw thru that.