glass "striking" to opal question

[Rosanna Gusler]

a friend of mine is having issues with a translucent white oceanside sheet glass "striking" to
opaque. it is doing this at 1150f during bending. here is the fb thread : https://www.facebook.com/barbara.cas...tion&ref=notif ......my question is related to this statement "Opacification and color striking are two different things and happen independently of each other. " is that so? and why or why not? thanks. r. EDIT: !!i should have titled this striking to OPAQUE not opal.

[Pete VanderLaan]

I won't go to facebook but I can talk about these two issues which are separate ones.
First Color: There are colors that strike on heating and cooling and heating again. Silver and copper bearing glasses are most notable and do so with colloidal suspensions which are stringy long molecules forming in the glass. They usually appear colorless initially but begin to get organized after a few heats.
Opalescent glasses are not the same as opaque enamel glasses so I'll just address opals. They are formed two different ways, one with fluorine and one with Phosphorous. Seeing phosphate glasses in sheet form is just not very common but they exist. Fluorines are the most common and they turn a strong opal depending on the percentage of three things in the glass. Fist is the fluorine itself which does not create any opalescence at all unless it is in the presence of alumina and calcium which is turn create alumina fluoride and calcium fluoride crystals. They will not turn opal without it.

Phosphate opals are the result of phase separation between a silica and a phosphate glass. Silica is not the only network former out there.

In my world, opalescents tend to become a dense opal right after the are drawn from the pot. As time goes by, these glasses grow these crystals and the crystals collapse and then grow again, getting a little weaker each time. Usually by the fourth day in a pot, they are losing their opacity.
Profoundly caustic in a pot, the raw bathes are nominally melted at about 2050F if you want to hang onto your pot at all. They will also eat electric elements which your friend may want to take note of.
Does that do it?

[Rosanna Gusler]

Ok. Thank you for that now how about opaque? This glass is going from a translucent white to opaque white and only on parts of the sheet. This is Barbara Cushman of glasstile. She is no newbie to firing so the reporting is solid and I did see pics.

[Pete VanderLaan]

Initially I would say the formulation wasn't mixed well. They might have wanted a "Streaky"
These density strikes in sheet glass have a sheet being cooled before it can entirely get its molecular house in order. That's true to a great extent for strike colors as well but the reasons are a bit different.

It might be the case that if it could be fired and crashed quicker the strike would have less time to organize. It also could be that other sheets of the stuff have different makeups and may behave better ( or worse) .

I have a fond memory of dear friends in Lubbock, Chuck and Melanie Berg who called me about this stuff and while Melanie was seeking her answer, she didn't say why it was an issue but being sensitive, I pressed her.

She had this window she was making, and the Bergs worked on stuff that could be up to 40 feet tall and she said it was a problem with the cows.

OK, the hook was set.

"The cows?" I said and she said, "their hay". "Um OK I said tell me more". "Their hay keeps turning red. That's not good."

We worked it for a long time and Melanie spilled the beans that it was a commission for some very religious guy in Lubbock whick is chock full of religious guys who had a mess of Black Angus cattle and he wanted a big F***King window in his mansion with the cows grazing and the hay kept turning red. Chuck and Melanie only worked in Dalls from Blenko and had the biggest stash I've ever seen, virtually thousands of them . The glass in Question was a strike for color glass that usually behaved. This didn't. It was a very nice wheat tone when they started and in firing the stuff turned a really nice red but hay isn't red. Blenko would have sold it for a lot more if they thought for a minute that it would turn red.

I'd like to tell you this ended happily but actually, no, the glass is going to do what it wants to do given its built in DNA. She got some improvement firing it a lot faster and colder. Other dalls behaved better.

Faster and colder may help your friend. Considering a career switch is of course another option. Opals do what they gonna do if the DNA is right. And we think glass is nice and stable if it doesn't drip on the floor.

I miss Melanie and Chuck. Quite the couple.

[Rosanna Gusler]

i screwed up the title to this thread. i got my O words twisted. the glass is "striking" to opaque. not opal. but i am loving the chemistry and other stuff so win win. thanks.r.

[Michael Ahlefeldt-Laurvig]

[quote=Pete VanderLaan;152563]Initially I would say the formulation wasn't mixed well.
These density strikes in sheet glass have a sheet being cooled before it can entirely get its molecular house in order. That's true to a great extent


Your answer is vey funny

[Pete VanderLaan]

Originally Posted by Rosanna Gusler

i screwed up the title to this thread. i got my O words twisted. the glass is "striking" to opaque. not opal. but i am loving the chemistry and other stuff so win win. thanks.r.

****
I define these types differently. The opals at lower percentages will make a translucent opal. In high enough percentages ( over 6.5%) are going to be pretty much opaque or, You can't see through them but they fail the definition.

True opaques like enamel whites are made with Arsenic and lead. It could be Antimony and Lead but most anything running out a single valence point is going to do it. The true opaque usually doesn't even have 50 percent silica in them. The opaques Mark made are profoundly high in alumina- as high as 20% and include titanium at high percentages as well. I'm going to pursue substituting titanium for silica in the fluorine glasses I'm deeply involved in right now. But not now. Right now I need a solution.

[Michael Ahlefeldt-Laurvig]

I have a fond memory of dear friends in Lubbock, Chuck and Melanie Berg who called me about this stuff and while Melanie was seeking her answer, she didn't say why it was an issue but being sensitive, I pressed her.

She had this window she was making, and the Bergs worked on stuff that could be up to 40 feet tall and she said it was a problem with the cows.

OK, the hook was set.

"The cows?" I said and she said, "their hay". "Um OK I said tell me more". "Their hay keeps turning red. That's not good."

We worked it for a long time and Melanie spilled the beans that it was a commission for some very religious guy in Lubbock whick is chock full of religious guys who had a mess of Black Angus cattle and he wanted a big F***King window in his mansion with the cows grazing and the hay kept turning red. Chuck and Melanie only worked in Dalls from Blenko and had the biggest stash I've ever seen, virtually thousands of them . The glass in Question was a strike for color glass that usually behaved. This didn't. It was a very nice wheat tone when they started and in firing the stuff turned a really nice red but hay isn't red. Blenko would have sold it for a lot more if they thought for a minute that it would turn red.

That’s funny