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Mark J

Blackened Glue Line

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I am posting this question here for greater visibility.  I am using Titebond Quick and Thick for my project in the journal section that involves gluing up layers of veneer.  Things have been going well enough, but this morning when I took the stack out of clamps I was surprised to see that the last glue line had turned black. 

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And another corner:

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Quick and Thick dries clear, so this is completely unexpected.

To be honest it looks like mold, but I've never heard of a PVA type adhesive supporting microbial life (although I do remember a kid in grade school who had a habit of eating paste).  My immediate suspicion is the container of water I have been using to clean the roller of glue between applications.  Didn't see anything obviously growing in the water, but spilled it out and washed the container.  

I'll give Titebond a call on Monday, but I would  appreciate any thoughts on or experience with this you may have to share.    

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It just occurs to me that that particular piece of veneer had some heavy pencil marks on it.  Could the glue have disolved the graphite and carried it out with the squeeze out?

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Probably. It'll probably go away when you clean the side up. I know i've seen some bad looking glue lines disappear as soon as i hit them with some sand paper.

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1 hour ago, Chestnut said:

Probably. It'll probably go away when you clean the side up. I know i've seen some bad looking glue lines disappear as soon as i hit them with some sand paper.

Probably graphite or probably mold?

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1 hour ago, Mark J said:

Probably graphite or probably mold?

Mold doesn't make sense. Graphite from the pencil makes a lot more sense. The other thing is a reaction between something in the wood and something in the glue but then you'd think it'd be on all of them. So it's probably graphite.

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Did the clamp bars happen to touch the wood at those points? Woods with fairly high tanin content often stain when iron or steel touches them in the presence of moisture. Might be some acids in the glue that accelerate the process.

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That looks very limited. Is it only this one spot or many? I seriously doubt it is the glue and suspect a contaminate. 

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I am more and more convinced this was graphite from the pencil marks.  In fact if you look at the darkest "stain" it's shiny like graphite.

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I had never heard of migration of pencil lines, but did a google search.  There have been some artists that had issues, but that was all I found.  Also, I have absolutely no experience with this particular glue, but it appears to be some different composition than others that we use so much.

It would be interesting to do a small test on something else, using the same pencils and glue.

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22 minutes ago, Tom King said:

It would be interesting to do a small test on something else, using the same pencils and glue.

You read my mind (or I read yours).  I used the same pencil to make heavy lines on some scrap veneer.  Rubbed the glue into the pencil mark.  Now I'm waiting for it to cure, but at least initially it didn't seem to remove the pencil marks.

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So here's the pictures:

Heavy pencil marks.

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Glue blob applied and thoroughly mixed over the pencil marks.

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Almost completely cured.

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As you can see the pencil marks are not smeared or diminished and the glue did not go black.  I'll look at this again tomorrow, right before I call Titebond to discuss.  

 

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I don't know, it could have been that the pencil mark was right at the edge of the piece and is showing through the glue.  I don't think it is going to be a problem after filing and sanding, but it sure is curious.  

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Maybe it will never happen again.   Maybe something fell into the glue before it dried.

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It's one of two things - either a contaminate or a chemical reaction.  I'd go with the later.  Something in the wood or some other particulate got into the glue and caused a reaction that turned black.  Haven't a clue what it might be although the suggestion that it was steel of some sort is the one that makes the most sense as that typically goes black.

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Due to the complexity of this build, that little black mark will probably be the least of your concerns. This will be a cool project! 

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