Nice Owen. The hide glue acoustic question permeates guitar and violin forums as well. There has been  one rather extensive test that concluded a specially formulated aliphatic resin for its acoustic properties served as a filter giving a more harmonic spectrum. The problem I found with this test is that it was dependent on a wood sample glued to metal. What has been taught to me is that what makes hide glue superior in ever so many ways is its long chain molecule bonding. In this way it is closer in nature to the cellular properties of the wood than any synthetic. The only thing I have ever been able to find in reviewing the acoustical journals has to do with gelled gelatin in circuit board use. Irrelevant but they liked it. 


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> On Mar 4, 2016, at 7:22 AM, Owen Daly <[log in to unmask]> wrote:
> 
> I haven’t read Paul’s account of the crisp stiffness of hide glue relative to the rubbery energy-sink traits of stuff like Titebond, but what was paraphrased is consistent with my experience. Know that hide glue doctored with stuff like urea, in order to slow the gel-time, is also rubbery in texture. If you drop a blop of undoctored hot hide glue on, say, some waxed paper or the like, and let it cure, and do the same with hide glue retarded with urea, you’ll find the first blop very rigid and the second one quite flexible and rubbery. There’s more to the behavior of glue than raw ‘strength’ against failure.
> 
> That said, one chooses between these things depending upon context. I rarely use urea to retard hot hide glue, but I when I do, I have a purpose. Where might one WANT strength tempered by flexibility or rubberyness? Well, when “breadboarding” a big panel, like the front of a lid of bottom panel (full-length bottom on something like an Italian or German instrument), using a long tongue-and-groove joint, across the width of the panel, the slight flexibility of urea-treated hide glue (or the use of something like Titebond) allows, while imparting and retaining flatness of the panel by the rigidity of the length of the batten, for some give and take as the panel expands and contracts in width with changes in relative humidity. There’s one place. Another is in gluing small decorative moldings where stiffness doesn’t matter.
> 
> It is more difficult to justify and make up some “reason” for the acoustical improvement imparted to a soundboard which has been properly sized with undoctored thin hot hide glue than it is to experience it first hand, comparing the sound of the board in the raw, to the response it yields, to even the most cursory handling, after the size has cured properly. There are other reasons to size boards, of course, not least of which is the reduction of the liklihood of various glue joints failing from glue starvation (the main glue soaking too deeply into the porous and thirsty dry raw wood), and the much less stain-prone cleanup of glue squeezes, that sort of thing.
> 
> Lest the use of size, not just on soundboards, but on other components, seem like a silly modern “magic Stradivarius-style bullet” affection, it is important to realize that the pre-sizing of things to be glued was a universal practice in the old days (up through the beginning of the 20th century). It stabilizes things before gluing, and the imparting of greater stiffness/elasticity to a soundboard was probably originally merely a fortuitous beneficial side-effect to a practice deployed for other purposes. It accomplishes a lot.
> 
> It doesn’t hurt, in exploring this, to have a reasonable amount of experience listening up close to harpsichords made by the not-inconsiderably number of instrument makers who use the practice routinely.
> 
> It’s silly, of course, to get one’s knickers in a twist about this, but in my experience heartfelt resistance and skepticism to the practices used by many experienced makers  (nobody in these postings has expressed such an attitude) is usually motivated primarily by the unwillingness to learn how to use the material competently. For many it’s just too much trouble to learn to be comfortable handling real hide glue, so the answer is often “I use other stuff and mine’s just plenty good enough.”
> 
> 
> 
> ____________________________________
> 
> 
> Owen Daly Early Keyboard Instruments
> 557 Statesman St. NE
> Salem, OR 97301
> http://www.dalyharpsichords.com
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> 
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Note:  opinions  expressed on HPSCHD-L are those of the  individual con-
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versity of Iowa.  For a brief  summary of list  commands, send mail to
[log in to unmask]  saying  HELP .
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