Official Luthiers Forum!

Most people may already know about this, but I had never encountered this problem, so I thought I'd post this.

Recently I sent an ebony fretboard blank to Andy Birko for slotting and profiling. Andy's work was great! However, the re-surfacing exposed numerous small shiny spots, as shown in the picture (left side, top picture). Scraping the back side, I found that the spots went all the way through. I tried removing them with solvents (alcohol, mineral spirits, naphtha, acetone) and hiding them (Watco oil, Feibing's dye) but nothing affected them. Remembering threads on OLF about removing white mineral stains from rosewood with hydrofluoric acid [edit: should have written "hyrdrochloric acid"], I put on nitrile gloves and tested some "Masonry Cleaner" that was sitting in the basement, left over from some project a few years ago.

Each little spot bubbled under the wet layer of acid solution. With the help of some back-and-forth with a rag, the spots disappeared. Not knowing if it was necessary or not, after wiping the area with plain water I applied a solution of baking soda and water to neutralize any remaining acid.

As the pictures show, this method seems to work well.

_________________
Tim Allen
"Never hurry, never rest."

That sounds extremely dangerous and in the case of committing a little mistake the price could be much higher than a lifetime supply of the finest CNC shaped and slotted ebony fretboards.

It's very common for ebony to have mineral deposits in the grain of the wood.
Minerals don't take stain well....

_________________
"Act your age, not your shoe size" - Prince

Markus' point that acid solutions can be dangerous is a good one. If you aren't sure you can keep the solution away from your eyes and skin, don't use it. Dilute solutions of hydrofluoric acid are used for a variety of purposes, most importantly removing rust and mineral deposits, and are widely sold in grocery stores and hardware stores for this purpose. For safety, it's important to follow the directions on the package. Like sharp edge tools, table saws, solvents, and some other things we use in lutherie, the usefulness outweighs the potential dangers when used properly.

_________________
Tim Allen
"Never hurry, never rest."

I could be misremembering, but I would have thought masonry cleaner was muriatic acid. If it is flouric acid, be careful.

http://en.wikipedia.org/wiki/Hydrofluoric_acid

Scroll down to the pictures. Gross.

Mike

_________________
Mike Lindstrom

Mike is right. Hydrochloric, not hydrofluoric. Less dangerous. I just put a bracketed edit in the text of the first post.

_________________
Tim Allen
"Never hurry, never rest."

You'll be OK with some basic precautions with hydrochloric acid, all of you have been carrying around a bunch of it in your gut your whole lives

I've seen those spots on a lot of ebony in the last few years. I thought they were contaminated dust or something until I started processing blanks that came in far away from anything that had ever touched coolant. That board looks a lot like a big order I sent out last year...did you get it from another builder?

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Hydrofluoric acid can penetrate skin and dissolve bone. ...bad stuff.

_________________
Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Hydrofluoric acid can penetrate skin and dissolve bone. ...bad stuff.

_________________
Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com