sodium_stearate - 9-12-2017 at 10:27
This is about the topic of "reversible adhesives".
One such glue was an old brand from about 100 years
ago called "Stratena", which was a clear cement that takes
many hours to dry because of having water in it.
As a bit of background on all of this: The recording heads
used 100 years ago to record sound on Edison cylinders
made use of this glue to hold some of the critical parts
together. One reason this type of glue was chosen, is because
it is easily removed so that small mechanical changes and adjustments can be made to the unit.
Taking apart a glue joint cemented together with gelatin-based
Stratena glue just requires placing a wet Q-tip on the parts
to unglue. Leave it soak for about 15 minutes and it
completely releases.
A few years ago there was a guy making and selling new
little bottles of Stratena on Ebay. It was good stuff, it works
fine. But he stopped making it.
He did tell me on the phone one time a few details about
how he was making it:
He said he was using "Jello" brand gelatin from the grocery
store. To this he added distilled water, boric acid, and alcohol.
For the alcohol he used vodka, which he also liberally
imbibed in all the while he was cooking his Stratena glue batch
on the stove.
This is all I currently know. One more detail from the old
days is that they used pure gelatin from sturgeon bladders,
a substance sometimes referred to as "isinglas".
The fellow making the glue told me that since sturgeon bladders seem to be in rather short supply and hard to
come by, he settled for grocery store "jello" gelatin.
Seeing as how he no longer makes this unique glue, and seeing as how it is in demand for those who want to
rebuild and use the old Edison cylinder recorder units,
I am currently pondering making some test batches
of Stratena myself, based on the sketchy and incomplete
info I have.
Now for my thoughts to bounce off of you all:
1) What might the boric acid and the alcohol be doing?
2) I understand the basic idea of a gelatin/water solution
evaporating and leaving gelatin as the adhesive, but do not
understand what function the other ingredients may have.
3) Any ideas or comments?
4) I suppose that a few trial batches and lots of testing
might be the only way to figure it out.
Sulaiman - 9-12-2017 at 11:38
According to Wikipedia, Isinglass was used as a glue but is not gelatin https://en.wikipedia.org/wiki/Isinglass
In the '60's it was very common here amongst home brewers but I preffered patience.
I suspect that, unless you can find the recipe, a lot of experimenting will be required.
Once you have determined the optimum recipie for your glue,
consider more humid/drier/hotter/colder climates if you want to sell it.
As for the actual chemistry ... it is beyond my knowledge 
Bert - 9-12-2017 at 11:42
Boric acid Is probably a preservative, microorganisms will otherwise be happy to eat wet jello. A lot of the old protein glues used an alkali to
modify the proteins and make it less reversible under damp conditions, the boric acid may also help keep the glue from going permanently hard under
mildly basic conditions?
The alcohol keeps the glue liquid after cooling, otherwise protein glues of this general type were applied hot from a glue pot. It is the primary
difference between similar protein based hot pot glues and cold applied bottled liquid glues if you look at the old formularies.
Protein glues characteristics have a good bit to do with the particular amino acids they contain, the fish based glue may have had different
characteristics than the (cow based, I believe) gelatin glue.
Look at traditional book binders/repairers and musical instrument restoration sites, they use some of the same technology.
My teacher used hide glue poured liberally on the paste wrap of cylinder shells around where the spolette (rammed hard black powder in a cardboard
tube, traditional fuse) entered the shell. He said it penetrated paper and cardboard better than more modern glues such as PVA white glues. Also, he
ran a printing company as a day job- and they had a good bit of it from the old days. Along with grinders for the solid glue, water jackets hot glue
pots & etc. I use the liquid hide glue sometimes, not having the old equipment or materials.
(Edit)
You can find pure powdered isinglass on eBay, made from fish swim bladders. The stuff used by brewers has Sodium metabisulfite as antioxidant (and
mallic acid for I don't know what purpose) added, but is also mainly collagen from swim bladders of fish.
https://m.ebay.com/itm/ISINGLASS-POWDER-2-OUNCES-56-GRMS/263...
[Edited on 9-12-2017 by Bert]
LearnedAmateur - 9-12-2017 at 11:49
Well boric acid is used to cross link polyvinyl alcohol/acetate chains (the PVA glue slime of many a scientific childhood) so from my understanding,
it would strengthen the gelatine and make it a better adhesive. As for the alcohol, I'm not sure, my guess would be so that it's easier to apply,
faster evaporation thus drying time, or a combination of both.
unionised - 9-12-2017 at 12:28
I'm guessing this is a similar sort of thing.
Does it help?
http://www.woodcentral.com/woodworking/forum/archives_handto...