bullseyeglass.com • View topic - uroboros & bullseye cullet: compatable?

uroboros & bullseye cullet: compatable?

For discussion of processes related to using Bullseye glass, including kilnforming and kilncasting, torchwork, blowing and stained glass.

uroboros & bullseye cullet: compatable?

Postby jonnieburrito1 » Mon Aug 23, 2010 7:13 am

After annealing a 20" dia by 7/8" casting using Bullseye crystal clear casting cullet (90 coe) and uroboros clear casting cullet (pail of broken up double rolllled clear), I was surprised and annoyed to discover that what appears to be compatability fractures developed over the next week or so. These cracks form a netwiork of fractures around the outside 1/3 of the disc and are not like annealing flaws I have had with a "S" shaped crack running all the way across. Could it be that the Uroboros shovel guy scooped some non-90 coe stuff into my bucket, or is Uroboros just not that good a product to use in thick castiings? (I followed Bullseye's latest anealing bullited carefully, so I don't think it was me.)

Needless to say, the casting was really nice!


Re: uroboros & bullseye cullet: compatable?

Postby marykaynitchie » Mon Aug 23, 2010 9:12 am

Hi John,

First off, let me say that I am sorry you had these results. I don't know the precise cause, but I can provide some background on glass manufacturing that might help you avoid these results in the future.

The Bullseye cullet that you used is graded as Bullseye Compatible F grade. In a nutshell, we never describe our compatible glasses as "COE (coefficient of expansion) 90", because that would not be accurate. Our tests (and the tests of other manufacturers of fusing glass to our knowledge) do not actually test for COE. Our test is more basic: it shows us whether each small lot of glass will work successfully with any other Bullseye Compatible glass in the kiln.

Our glass is designed to be compatible with all other Bullseye Compatible glasses. We don't recommend that Bullseye glasses be combined with glasses from other manufacturers, because we can't know or speak to the consistency of testing protocols that are not conducted under our roof, or under our supervision. At this time, Bullseye is the only company that makes Bullseye Compatible glass.

Some dealers carry multiple brands of glass, and describe some of these as "COE 90", but we find that use of the term "COE 90" to be less about science and more about sales-speak. Sometimes using the glass of two manufacturers together works. And sometimes it doesn't. So when you mix the glass of two unrelated manufacturers, the factory testing that you paid for to both the manufacturers is no longer valid, and you need to do your own testing to ensure good results.

For a more detailed report on this very topic, you might be interested in reading this article by Bullseye's owner, Dan Schwoerer: http://www.bullseyeglass.com/pdf/techno ... tes_03.pdf

Re your other questions, I can't speak to the casting quality of Uroboros glasses or what the Uroboros guy shoveled into your bucket.

Let us know if you decide to cast your project again, with a single brand of cullet!

Mary Kay
Mary Kay Nitchie
Bullseye Glass Co.

Subscribe to Bullseye kiln-glass videos at
Posts: 1205
Joined: Thu Oct 13, 2011 5:39 am

Re: uroboros & bullseye cullet: compatable?

Postby Twin Vision Glass » Mon Aug 23, 2010 6:50 pm

Do you have a photo of the piece :?: and what was the configuration of the kiln you where using.(top fire/side fire :?: Many questions can result in hopefully some answers for you. Perhaps a good question tooo is what day did you get the cullet from Uroboros . They would be able to tell you alittle more about the batch and cullet from that day. What was your firing schedule as well, and did you let it cool before opening . :?: Although I am sure you did. It is strange that it is just having problems around the outside edge if I read that correctly (and if not , sorry!) Anyways, abit more info would be super..
Leslie Rowe-Israelson
Give out FREE hugs!
Twin Vision Glass
Posts: 567
Joined: Wed Feb 04, 2009 4:42 pm
Location: Invermere , B.C. Canada

Return to Technique

Who is online

Users browsing this forum: No registered users and 1 guest