Contamination-Specks on cherry ply

[Michael Panis]

Hi Folks,

I've had the following happen to me two times, and I'm hoping someone has some idea what is going on.

I sand cherry plywood (120-220 grit), spritz a little distilled water on it to raise the grain, and then when I go to sand down the grain, I notice that the whole board is covered with black specks. They are about the size of a period at the end of this sentence. It doesn't seem to affect every board. I can sand it down, and it won't come back.

I also had the specks appear when I applied some shellac.

Does anyone know of a contamination that can cause this?

---Michael Panis

[Russ Buddle]

What sort of sprayer are you using? Is it clean inside?

[Michael Panis]

Hi Russ,

Thanks for responding. The sprayer is a basic pharmacy water sprayer. It's never been used before. I don't think it is the water or sprayer, though, because some boards show the problem and others don't.

---Mike

[Howard Acheson]

Why are you raising the grain? What finishes are you planning on using?

[Michael Panis]

The plan is shellac, followed by alcohol based dye, followed by more shellac. I'm raising the grain and then sanding it down because that's what I was taught in a Woodcraft course on finishing that I took this year, and we ended up with some beautiful sample boards at the end of that class.

[jerry cousins]

i use shellac all the time for finishes and sand a bit between coats - maybe forego the water spray and just sand down after the shellac coat - which will also raise the grain a bit.

jerry

[terry hansen]

The black spots seem to indicate an iron reaction, a search on google gives this on the web and may provide a clue (as it's written by Jeff Jewitt I tend to believe it.)
http://antiquerestorers.com/Articles/jeff/using_wood_bleach.htm
"Oxalic acid is unique in that it will remove a certain type of stain formed when iron and moisture come into contact with tannic acid in the wood. Some woods like oak, cherry and mahogany naturally contain a high amount of tannic acid and a black stain is formed when the wood gets wet with tap water (tap water contains iron as a trace mineral)."

This seems to indicate you have some iron on the wood that is reacting with the tannic acid and distilled water. Maybe try cleaning with oxalic acid prior to wetting and the rest. I'd probablly email Jeff at homestead finishing (check his site) and ask him as I've followed his suggestions and had great results.
I'd be interested in reading about your results.

[Dan Forman]

You might try using distilled water.

Dan

[Jim Becker]

You don't need to raise the grain before shellac...just do your first application, let it dry, and lightly sand off any "whiskers" with 320 wet and dry. But if you do raise grain for any reason, Dan is correct...you should always use distilled water, not tap water. Buy a gallon and keep it in the shop for this purpose...it will last a LONG time.

[Michael Panis]

The black spots seem to indicate an iron reaction, a search on google gives this on the web and may provide a clue (as it's written by Jeff Jewitt I tend to believe it.)
http://antiquerestorers.com/Articles/jeff/using_wood_bleach.htm


Thanks. I suspect you are right--that it is iron from something reacting with tannins in the wood. I'd prefer not to apply oxalic acid since it doesn't always happen.

I'm not sure the source, since I've been using a distilled water. My best guess, though, is that even though I have been using clean rags to apply the finish, I wiped down the water with rags made from old T-shirts that have been through the laundry a few times.

Thanks again, and I'll post more if I discover something.