Thickening Glastac

Today I want to have a short chat about my experiences with Bullseye’s Glastac and some experiments with using CMC to thicken it. There’s no rocket science. I simply though you might enjoy another way to make use of your CMC.


If you’re a glass fuser you’ve probably used Glastac. If you haven’t I recommend you try it.

Glastac is a deliberately weak glue and in my experience it cleanly burns away in a kiln. It is useful because you can glue together the component parts of your glass masterpiece with the certain knowledge that you can re-place the parts for quite a long time. Better still, it helps to ensure your masterpiece will not fall apart when you are moving it to your kiln.

As an aside, I caution against using white PVA glues, such as the oft-recommended Elmer’s Glue. Although I do use PVA glues occasionally, I have noticed that it does not always cleanly burn away and that it can cause damage to a glass surface. I particularly notice this when an excess of PVA is used. But I digress.

The only problem I have found with Glastac, particularly when used in excess, is that surface tension sometimes drags small pieces of glass away from where I put them. Using less Glastac helps avoid this problem but the converse situation is that sparing use of Glastac means that the small pieces of glass are not sufficiently glued to stay put.

And then I noticed that Bullseye had introduced Glastac in a gel form. Hmm. Thinks. Can I find the Manufacturer’s Safety Data Sheet (MSDS) to find out how it differs from the “old fashioned” Glastac? No, so it’s time to just experiment.

Avid readers amongst you will remember that I’ve chattered about carboxymethylcellulose (CMC) on a number of occasions. Most of my chatterings were in Squirt Your Frits but I’ve also mentioned it in passing in other places such as converting ordinary safety flux into a gel form over at Make Your Own Safety Flux.

This made me wonder if a little CMC gloop would thicken “old fashioned” Glastac and make it even better.

Thickening Your Glastac

dscf3558-glastacInstructions on where to find CMC, what it is, how it works and how to make your own CMC gloop is covered in plenty of detail over in my Squirt Your Frits blog. I will not repeat all this information so read that blog and come back again if you need to. I will however show you pictures of a bottle of Glastac and (lower down) a little 100 gram pot of CMC sold under the “Tylo” brand name typically bought by sugar crafters.

Making your own substitute for Bullseye’s Glastac Gel is a simple matter of thickening up some “old fashioned” Glastac with CMC. However the devil is, as they say, in the detail.

I found it most convenient to start by making up some “sloppy” sol-phase CMC gel. The exact consistency does not matter. All you are aiming for is a CMC gel that is thick but flows reasonably slowly when you tip the container.

dscf3555-cmc-potNext, you need to find another little container and add some Glastac to some CMC gel and give it a thorough mixing. If the outcome is too thick, either add some more Glastac or add some water. If the outcome is too runny add some more CMC gel.

As to the exact proportions of Glastac and CMC gel I can only report that making numerous little batches with differing proportions didn’t make seem to make any noticeable difference. As long as there’s a reasonable amount of Glastac in the mixture it’s going to be a glue. As long as there’s some CMC gel in the mixture it’s going to be thicker.

What could be simpler than that?

Speedy Gel?

In an attempt to make the homemade substitute dry quicker I tried using propanol in place of some of the water.

There’s nothing special about propanol (also known as isopropyl alcohol). It’s just an industrial alcohol  that is widely used as a solvent and as such it’s also useful for cleaning glass. Having said that, I mostly use acetone for cleaning glass.

However, unlike the ethanol (also known as ethyl alcohol) in your booze, it’s not safe to drink. Here in the UK I buy it from APC Pure rather than from glass suppliers simply because it’s much cheaper and they’re relatively local. I’m not connected with APC Pure other than being a customer. And once again, I digress…

I didn’t notice any adverse effects of using this modified mixture other than the smell of evaporating propanol. I can’t really say that I noticed the glue drying noticeable quicker but to be fair I wasn’t conducting a proper controlled experiment against a stopwatch.

So, I leave you with the thought that using an alcohol, such as propanol, should quicken the rate at which the glue dries but no convincing practical evidence. This is a prompt for you to continue the experiment and tell me!

Homemade Glastac Gel In Use

Although I have not compared this homemade Glastac gel mixture with the genuine  Bullseye’s Glastac Gel I can at least tell you that I’ve had good results with the homemade substitute (with or without adding alcohol).

The homemade mixture still works as a weak glue. The improvement is that it no longer seems to cause little glass pieces to slide and shift as the glue dries. Other advantages are that it’s quick, easy and cheap to produce in small quantities and you don’t need to find more space for yet another bottle of glue.

If you find your homemade Glastac gel mixture works well you might consider buying some of the real Glastac Gel. At the worst it’s going to be no better. At best it’ll be even better.

Shelf Life

I found that leaving a small open pot of my homemade Glastac Gel substitute lying around for several weeks resulted in an “infection”. The feint tint of green near the surface leads me to suspect the beginnings of algal growth. Maybe I’ve discovered a new balanced diet for bugs. Hmm.

But all is not lost. Simply make up your homemade Glastac gel mixture in small quantities when you need some.

This does not mean you have to make up the CMC gel in small quantities. There is a shortcut. You may recall that I’ve already mentioned in Freeze Your Frits that your CMC gloop will freeze successfully. Store your excess in the freezer and make use of it a little at a time.


That’s all folks.


About chatterglass

Maker of stained glass frippery.
This entry was posted in CMC, Experiment, Glastac, Tylo and tagged , , , . Bookmark the permalink.

2 Responses to Thickening Glastac

  1. george a says:

    Adding a small amount of benzyl alcohol might well prevent the algae. Probably will not affect glue.

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