Calcium cone 6 liner glaze part 1 (crystal?)
For the past few months I have been in love with a liner glaze used by artist Susan Filley. I want one of my own, one problem though, I have no idea how to make calcium crystals, hell, I don’t even know if they are crystals in the traditional sense or if they are just a semi matte glaze held for a long tie .But I know crystal glazes usually have base line attributed like low alumina, silica, and enough of whatever makes the crystals. CMW insists that any Alkaline earth flux can make crystals if done right. I consider iron to be an AE, so I can make iron crystals. I know calcium is an Ae flux so I must be able to make calcium crystals. One problem, I have no idea or experience with calcium crystals. So the journey begins to figure out the molar amount of calcium, silica, alumina, flux, XYZ XYZ that is needed to nucleate the crystals.
For my first round of tests I did something I don’t usually do. I made 3-4 different shots in the dark based on my experience with crystal glazes in general.
A high alumina calcium glaze with a base line of five ingredients. I wanted the glaze to be as simple as possible. This was named Calcium liner #1
A Bristol glaze with little to no boron. Usually cone 6 glazes need boron in them as a low temperature glass former to bring the temp of the glaze down to cone 6. This glaze was named crystal Bristol (I am cleaver and no one else would have ever thought of that name)
A glaze I can play around with. Named this one matt rework. At some point I accidentally made calcium crystals…. Kinda. I really made a matte glaze and dumped a bunch of Titanium Dioxide in and it somehow worked. To this day I am not sure if the TIDI was killing off the crystal nucleation (because I used alot) as TIDI likes to do, or if It was just a crappy matt glaze.
Two things I need to confirm in my tests. Firstly I need to know if i can just load up a glaze with Calcium and it’ll happen. Secondly I need to know how much the alumina and silica can be played with. The first question is important because most crystal glazes have two AE with one of them being dominant. So the big question is, do I need calcium and magnesium/ something else to nucleate the crystals ? That’s why I have three different tests going at once. For now, let’s look at the tests I have done as a base line.
Test #1 : Calcium liner glaze
Calcium liner glaze 1
SG: 1.48
3-4 second dip
clay: porcelain
cone: 5 (hot)
Notes: Had some luck with this even though it’s under fired. I think I just made a semi matt glaze. This has about 0.5 calcium in the UMF. I like it but I do not call these “crystals” in the way that we think.
Close up of last pic
Next lets look at the Bristol glaze.
Bristol test 2
Admittedly…. I’m bad at Bristol glazes. The only reason I am doing one is because I saw that Old Forge has a calcium crystals Bristol glaze and that means it can be done this way.
His had low silica and alumina with a Bristol effect. Very little boron. The glaze I made came out fine ( I did not copy his recipe, I take pride in not trying to copy other people) but no crystals .
#3: Matt crystal glaze. This one I had some luck with but there is a problem. Calcium is white… the glaze I am trying to make it clear….. even if I made the crystals HOW WOULD I SEE THEM?! For this test I chose to put a little but of color in. This one had a high amount of alumina and boron.
Wait…… Did I do it or are those just “matt crystals”…….I CAN’T TELL BY LOOKING AT THEM! that’s the problem! I would not have been able to see these without the back ground color. I also put it in a bowl.
Matt crystal 3
Application: poured in for about 3 seconds
SG 1.5
cone : 7 ox
clay: IMCO porcelain
It is crazed to all hell but you can see it too right?
I am finding some success but my big question no one can seem to answer is, am i making a matte glazes? or calcium crystals? or are they the same thing and I am conflating the two. If I spoke to a person who knew about this would they say “ matt glazes are crystal glazes technically” or would they say “ matt glazes are crystal glazes but calcium crystals are different from alumina forming into a lattice formation which is technically a crystal” Is there a difference and I’m just chasing ghosts? I don’t know.
