It cracked AGAIN!

[Risa]

for you English system users.....

…. take 1.25cm (0.5 inch) chips of all of the glasses that you are planning to use and place them on a 6.35 cm (2.5 inches) wide piece of clear test glass (Tekta or 1101) such that there is at least 2.5 cm (1.0 inch) of space between each chip and the edges of the glass.

[Morganica]

Dear friends,
As said before, I wrote a long letter to BE's department of Research and Education.
2 major things I'd like to share with you

a. BE does not have a chart for the change of viscosity in their glass, nor do they have a table of temp.s that indicate where the glass becomes incompatible.

b. BE recommends to do a test, its details I'll post in a minute - and to check exactly what happens with the glass one wants to use -
"…. take 1.25cm chips of all of the glasses that you are planning to use and place them on a 6.35 cm wide piece of clear test glass (Tekta or 1101) such that there is at least 2.5 cm of space between each chip and the edges of the glass. Then subject the test bar to the same heatwork that your process will subject them to. Include all firings. After each firing, view the tests for strain through cross polarized light – or see if they break. It takes a little time, but is much less painful than using a bunch of glass only to have a broken piece."
I got Ted Sawyer's permission to poste this here, only I apologise that the measurments are in metrical system - as it was basically written to me, who works in metrical system.
Can someone please translate those to inch system?

Personally , I am going to do so, and test as many glasses [colors] as I want to use.

Following the discussion here, I shall also target at a lower top temprature, between 1600 to 1650 not 1700. You read above that Dairy Queen even raises the temp. as "low" as 1480 - but stays 5 hours at that temp.]

I hope more people will participate and share their experiences - of which we shall all benefiet
[and excuse my terrible spelling]

yours,
with eternal gratitude,
Havi

I would think there would be too many variables (for each glass, the chart would need to map temperature, rate of heatwork, number of previous firings/amount of heatwork in those firings..against the same information for adjacent glasses) to make a simple chart showing incompatibility charts. Such a chart would be monstrous huge and complicated.

Heatwork, not just the top temperature reached, plays a role in compatibility and opacity shifts. 15 minutes at 1700 degrees can change the compatibility of a glass, but 5 hours at 1480 degrees might do the same. When you're doing your chip tests for compatibility, that's one thing to test.

The trick is to find the combination that delivers the effect you want for the least amount of heatwork possible.

[Dairy Queen]

Glass flows thicker at 1480 than at 1700- thus bigger hole needed.

[Havi]

I understand,

Thanks a lot



Havi

[Havi]

I think you would all be interested in the discussion on this very board, at

http://www.warmglass.com/phpBB/viewtopi ... 39800#wrap

Even though they are talking about combing, the discussion there deals with cracks that might have been created from ANNEALING.
Seems to me that there might not be a difference, as long as the process temp. is the same.

Would be interesting to compare - - - -


I'd love to hear your comments,

Havi