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Wood treatments by Stradivari and Guarneri


Bruce Tai
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23 minutes ago, Advocatus Diaboli said:

The titian has a back weight of 98.5ish grams, and a top weight of 66.6 grams with a bar according to some old notes of mine.  I'm not sure how anyone calculated the CT weight at 48.1??

CT scan is fuzzy voxelized object and the density is calculated by the sw for each voxel (color darkness is proportionate to density but the machine must be well calibrated with samples of known density) the edge voxels may be half air - half wood and their calculated density will be distorted. If those voxels are included in the final calculation, the average will be too low.

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1 hour ago, Advocatus Diaboli said:

The titian has a back weight of 98.5ish grams, and a top weight of 66.6 grams with a bar according to some old notes of mine.  I'm not sure how anyone calculated the CT weight at 48.1??

I can imagine that CT density may be a few percent off.

But 48.1 and 66.6 is night and day difference. 

I have never done violin CT. I wonder how reliable it is. 

So what is the lightest Strad top out there? Joseph curtin reported 54 and 55.5 grams without bass bar in a Strad magazine article if I remember correctly. 

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1 hour ago, Bruce Tai said:

I have never done violin CT. I wonder how reliable it is.

CT is reliable but problem usually is somewhere between the screen and seat.

There are various CT scaners, the modern micro CT are extremely precise (but expensive), the old common CT's are nowhere near that, something like 0.5 to 1 mm voxel size. You can approximate a lot even from such fuzzy data but the operator must know what he is doing.

 

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6 hours ago, David Beard said:

I thought I'd read the Titian has spots that are only 1.9mm??

On the Strad poster, there is one small spot on the back shown at 1.9mm.  On the top, the thinnest is 2.2mm.

5 hours ago, Advocatus Diaboli said:

The titian has a back weight of 98.5ish grams, and a top weight of 66.6 grams with a bar according to some old notes of mine.  I'm not sure how anyone calculated the CT weight at 48.1??

4 hours ago, Bruce Tai said:

48.1 and 66.6 is night and day difference. 

66.6g for the Titian seems devilishly high, unless the CT average density and/or thicknesses are way off.

I made one Titian model using .40 density spruce, with grads approximately .1 - .2mm thinner than the Titian, and it weighed in at 63.5g with bar.  I made one of my "small" model (extremely close to Titian dimensions) with .39 density wood, and the top with varnish and bar was 62.7g.

I heard from Bill Sloan that the last time his ex-Jackson (big G form, very high arching) was in for some repairs, the top with varnish and bar was weighed at 61.1g.  It's pretty thin, CT .34 g/cc density.

 

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61.7 g for the top without bar looks a bit high to me, but only by a couple of grams... assuming the thickness measurements are correct.  But it looks easier to believe than the 48.1.  If the top with bar is 66.6g, that would mean a 4.9g bar... quite heavy, but the Titian bar is very fat and tall.

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17 hours ago, HoGo said:

CT scan is fuzzy voxelized object and the density is calculated by the sw for each voxel (color darkness is proportionate to density but the machine must be well calibrated with samples of known density) the edge voxels may be half air - half wood and their calculated density will be distorted. If those voxels are included in the final calculation, the average will be too low.

I’ve done plenty of ct rendering, so I’m aware of that.  Still, that’s a pretty extreme amount!  

 

11 hours ago, Don Noon said:

61.7 g for the top without bar looks a bit high to me, but only by a couple of grams... assuming the thickness measurements are correct.  But it looks easier to believe than the 48.1.  If the top with bar is 66.6g, that would mean a 4.9g bar... quite heavy, but the Titian bar is very fat and tall.

I’m getting 98.7 grams for the back and 57.5 without a bar for the top from a ct scan.  There’s a bit of starburst from the fine tuner, so that could be messing with things a bit. 

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11 minutes ago, Advocatus Diaboli said:

I’m getting... 57.5 without a bar for the top from a ct scan.

That looks like the most reasonable number yet.

I'm curious what the Titian bass bar weight would be.  It looks massive... but that depends on what density was used.

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On 7/5/2021 at 6:24 PM, HoGo said:

Doesn't potash and alum generally desctribe the same thing? Potassium aluminium sulfate?

potash is various potassium salts (potassium hydroxide, potassium carbonate etc.)  derived from leaching wood ashes in water, so not the same thing as alum.  

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5 hours ago, Advocatus Diaboli said:

I'm getting .447 density for the Titian bassbar, and 4.46 grams.

Thanks.  Looks on the weighty side, as I expected... but with that high density, I'd think it would be even more.

1 hour ago, Michael_Molnar said:

RE: CT densities, volumes, and calculated weights.

I can’t find any error estimates. If so, that is not good science. 

I'd only trust the error estimates if they were blind calibrated to precise physical measurements.  i.e. do the CT calculations, then measure and weigh the plate and see what it really is.

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10 hours ago, MikeC said:

potash is various potassium salts (potassium hydroxide, potassium carbonate etc.)  derived from leaching wood ashes in water, so not the same thing as alum.  

The reason I say alum and potash is because they are fuzzy terms but historically accurate terms. Renaissance alchemists named chemicals that way for practical reasons and limitations.

Potash (pot ash) can be made from burning wood or grass. Depending on the temperature, it can be K2CO3 and KOH in different ratios. A lot of CaO may be present, but they can be removed by some means.  A purer kind of potash can be made from burning potassium tartrate (tartar, wine stone) or burning potassium bitartrate (cream of tartar). The product is called burnt tartar or Alumen faecis, high-purity K2CO3.  

Alum has many names in medieval texts but dyer's alum is almost always KAl(SO4)2. Ancients knew how to make highly pure synthetic KAl(SO4)2 by recrystallization. They also prepared NH3Al(SO4)2 similarly, also called alum. Natural alum may be  KAl(SO4)2 or Al2(SO4)3. Al2(SO4)3 was chemically produced in large quantities in the 19th century for industrial use. I think an entire book may be written about alum's history. I am just giving a very brief summary.  

 

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14 hours ago, Advocatus Diaboli said:

I’ve done plenty of ct rendering, so I’m aware of that.  Still, that’s a pretty extreme amount!  

 

I’m getting 98.7 grams for the back and 57.5 without a bar for the top from a ct scan.  There’s a bit of starburst from the fine tuner, so that could be messing with things a bit. 

That's good to know. Is this a recent CT measurement? 

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