Somebody explain to me what this is and why it could work. I am familiar with CA glue pinblock treatment and use it periodically.

But glycerin? I recall from high school science lab class that glycerin is a lubricant.

How can it work to tighten tuning pins?

CA is superior. Glycerin is unnecessary; don't bother.

Glycerin is hygroscopic in nature. It attracts water molecules and doesn't release them readily. More moisture in the pinblock means more friction. But it takes a while and CA is fairly instantaneous.

Glycerin however, is NOT highly toxic and doesn't require the use of fans and respirators while applying. CA, is not kind to your liver.

Like Kent said, though, CA works better.

Living in Colorado, I'm sure you understand the problems with low humidity.

There was a glycerin and something mixture, that some tuners used when I first started in '75.
The word I got that it worked by attracting moisture.
The problem as I understand it was, that it continued to attract moisture and ended up ruining the pinblock. I think it caused dry rot, or a variation.
I highly recommend the C/A treatment, I have used it in over 30, and just recently had a failure, on a previously treated pinblock. I am assuming that the previous stuff sealed the block, not allowing the C/A to penetrate.

Was the failure on a pinblock previously treated with CA? Or with something else?

It was glycerin and denatured alcholol. I used it for years but stopped using it many years ago when I discovered many times that it simply did not work or sometimes made some pianos worse.

I was threated with a law suit on one of them. Even though I mixed it correctly as I always did (can't recall what the mixture is anymore, it's been to long since I've used it) it made the pins 3 times as loose as they were before I started. I called in another long time fellow tech to talk to this customer and convince her that what I did was an acceptable practice and that I mixed it correctly. It worked but she never called me back. That was the last time I used it. Frankly, I do not recommend using it.

Some tuners swear by it. I think those that do, have not used it often enough to discover that sometimes it does not work and in the process, you do pretty much ruin the pin block.

You have to tip the vertical onto its back preferably with a piano tilter and let it set there for 10 days to 2 weeks while it soaks in. With C/A glue, you're finished in no time and there isn't much of a waiting period.

When I use the CA method for pin block restoration, I am very strict about the working environment. I explain to the customer that we need good ventilation during the time that I'm working. A gas mask is used during the process, and I don't tune the piano for another week, to allow the CA to cure and thus, for me to tune without having to wear the mask.

Extra care is taken to protect keybeds, carpets, etc. Piano movers have to be brought in for the 'reverse' method on a grand - placing the piano on its side and applying the CA to the underside of the pin block.

It's not a fun job, but I offer it to people who don't want to rebuild their piano simply to have tighter tuning pins.

But glycerin? Judging by the comments above, I don't see a reason to even try it. Obviously, it is an outdated and inferior method which no one should consider.

Glycerin is 'bug food'. Not suitable even if mixed with denatured alcohol. The alcohol will evaporate and the bugs will go to town. You might as well smear maple syrup all over your pinblock...

I have used glycerin mixtures a number of times, but CA only once. I prefer the glycerin mixture, but flush the coils with straight denatured alcohol after the treatment to prevent the mixture from forming rust.

The reason I prefer the glycerin is because of the feel of the pin. The treatment is done to pianos that are old, their strings have lost much of their elasticity and they are not worth restringing. I prefer a smooth pull hammer style when possible. The “clicking” pin feel that many seem to prefer a CA treatment for is not what I prefer, especially for pianos in this condition.