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I've read from a few sources that Macassar ebony is more stable than black African ebony. Since I am greatly interested in the subject of fingerboard stability I really held my breath hoping i've found a better wood for the FB.

I did a little test. I took 2 headplates, both old and kept at 45% for a long time; one African black ebony, another Macassar and I sanded them to a reasonably similar thickness. Then I glued them together and planed them very precisely to the same width and length.

The black ebony was more or less quartersawn, the Macassar half QS, half rift (ending at about 60 deg)

I weighted them on a precision scale (black 40.99 grams, Mac 35.39 grams) and then placed them in a "wet box" (making sure they are equally exposed to the water tray) for 4 days.

I took them out and weighted again:

the black went up to 42.17 grams - 2.88 % increase
the Mac went up to 36.59 - 3.39 % increase

Size: the length remained equal for as much as I can measure.
the width of the Macassar was more than the Black by about a business card - which can be probably assigned to the rift area.

The conclusion from these samples is that Macassar does not seem to be more dimensionally stable than black ebony. It might actually be slightly worse.

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Thanks for letting us know Alex of your testing Alex!

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

Alex: I have been using Macassar for my boards and have not had any trouble. LMI comments on Macassar saying it is less likely to crack compared to other Ebonies. Not sure how much one can intertwine stability and cracking, but certainly a fair amount.
Tom

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A person who has never made a mistake has never made anything!!!

I've just completed my first Macassar back and sides guitar and I was totally impressed with how elastic and split resistant the back offcuts were, even when flatsawn. Much much much better than many rosewoods or black ebony.

I was not saying it is bad or problem-prone, just that it does not seem to have less shrinking/expansion than black ebony. Which is about double that of rosewood.

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For neck stability (relief variation) our interest is mainly in long grain stability. So, Alex, if you still have some comparable samples of the two ebonies, maybe try working them to the same thickness and glue them together with epoxy to make a hygrometer. Then see how they bend.

FWIW, when I have measured long grain Young's modulus, Macasar comes out nearly double the black ebonies, fairly consistent over about half a dozen different samples. Macassar routinely comes out at ~25-30GPa.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

My two samples remained identical in length. I even checked the alignment with a magnifier.

As for stiffness, I just received two Mac FBs and they feel ultra stiff but they are also a bit thicker than average. I'll see how they feel when worked down to 7mm. I've seen blanks that feel stiff when thick (around 9m,m or so) but turn rubbery when thinned, and others that remain stiff.

I used to think African blackwood is the mother of all stiff fingerboards until one I planed the other day. Quite rubbery even if the density and grain fineness is greatest I've had so far.

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Now this is fun. I had these two test plates back in my 40% shop, right? This morning when I looked again at them I saw the black ebony has cracked...2" crack. The Mac is OK. They both almost returned to the initial weight.

Filippo, I think curly is the root of all evil. Of all my guitars, the only neck I had problems with was a curly black ebony FB. Not very stiff stuff. After 1.5y the customer came back with it backbowed and I had to refret it. He does have high humidity there but another built by me, and 3 other luthier guitars, all OK. It might help if you paint a fair amount of shellac in yours after it puffs up.

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