morgan
New Member
Darn...lot of good info on the old forum. Sad that it got unstable. But whadya do?
Posts: 21
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Post by morgan on Oct 19, 2015 6:48:14 GMT -6
I've been following Arnie's adventure in strike firing, though nowhere near as expertly or scientifically. I've been using your Fe, Mn, Ti, Li combo. The first few firings I was getting a really nice yellow (bg and crystals). Then when struck the would turn the bg to a pleasant chocolate and produce fine lines of chocolate in the crystals. Really liked it. Over a few firings the pre-strike results have shifted significantly and I can't seem to find a way back to the nice yellow. Not completely unhappy with the current results, but I like the yellow and the strike fired yellow. I've been using the same glaze recipe. Only change I made with one batch was to use yellow iron oxide instead of the original black iron oxide. I saw no difference in the migration to the pre-strike color shift towards brown/magenta/butterscotch. I switched back to the black iron oxide with no success getting back to yellow. I've tried to make sure my glaze thickness application is as consistent as I can make it. On a few pieces I've gotten a bit of the yellow near the bottom of the pot which led me to believe maybe my application was getting thinner so I paid more attention to the upper glaze thickness, but.... I did do some firing schedule changes to try to get back there, no luck. My most recent firing (last photo) was the exact schedule that produced the yellow. The beginning firings that produced the yellows WERE in July and August so obviously the kiln cooled slower. Perhaps that could account for some of it, but I started getting the darker colors while it was still pretty hot outside. The most recent firing was just the other day and starting temp was 59 degrees. Anyone have any thoughts? Nice yellow pre-strike Post-Strike Yellow pre-strike (sorry can't get this one to resize smaller on photobucket...wierd) Post-strike Evolved pre-strike Evolved post-strike Most recent pre-strike firing (center vase)
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Post by Arnie Benton on Oct 19, 2015 16:24:24 GMT -6
Hi Morgan - Keeping all variables the same - clay, glaze ingredients, firing schedule - I don't think kiln cooling rates once the kiln is shut off would affect colors - potters who 'crash cool' haven't talked about colors changing, I don't believe. All that's left I think is glaze thickness. Deeper colors would indicate thicker glaze. Having said that I have next to no experience with vertical forms and the amount of flowing that occurs - on my plates and bowls, I'd focus on glaze thickness. On vertical forms maybe take out the Li - could cause excessive glaze flow -
Arnie
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Post by tileman2 on Oct 19, 2015 16:47:00 GMT -6
Arnie:
Keyword - vertical. Glaze run off verses glaze pooling on flat work- or close to it. I have never been able to get the colors on horizontal as others do on vertical pieces.
Tom
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Post by mohawkpiper on Oct 19, 2015 18:11:33 GMT -6
What do your cones say about the firing you liked and the current not so liked firings?
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Kuba
Full Member
SztukKilka in Old Formu
Posts: 111
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Post by Kuba on Oct 19, 2015 23:10:42 GMT -6
Heat work or most probably glaze thickness
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morgan
New Member
Darn...lot of good info on the old forum. Sad that it got unstable. But whadya do?
Posts: 21
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Post by morgan on Oct 20, 2015 6:26:00 GMT -6
Hi Morgan - Keeping all variables the same - clay, glaze ingredients, firing schedule - I don't think kiln cooling rates once the kiln is shut off would affect colors - potters who 'crash cool' haven't talked about colors changing, I don't believe. All that's left I think is glaze thickness. Deeper colors would indicate thicker glaze. Having said that I have next to no experience with vertical forms and the amount of flowing that occurs - on my plates and bowls, I'd focus on glaze thickness. On vertical forms maybe take out the Li - could cause excessive glaze flow - Arnie Hi Arnie. Darn you for starting me on this exploration of strike firing!!!!! lol I had assumed that because I got a few pots with nice yellow just at the bottom perhaps my glaze application was too thin. I'll have to try going in the other direction. What you say makes total sense. Duh Not sure I want to take out the Li considering the heavy seeding that's there now. I prefer more ground than what I'm getting with that glaze, more like the green vases in the final picture is what I like. Was actually considering reducing the silica a couple percentage points to get a little MORE flow. But... one thing at a time, right. Thanks, Arnie. Morgan
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morgan
New Member
Darn...lot of good info on the old forum. Sad that it got unstable. But whadya do?
Posts: 21
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Post by morgan on Oct 20, 2015 6:28:01 GMT -6
What do your cones say about the firing you liked and the current not so liked firings? The cones have been almost identical, taking into account some minor schedule changes. The beginning and the end are the same...right at cone 10.
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morgan
New Member
Darn...lot of good info on the old forum. Sad that it got unstable. But whadya do?
Posts: 21
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Post by morgan on Oct 20, 2015 6:43:06 GMT -6
Oh... and I don't "dislike" the morphed color. Just a matter of learning to control things better so I get consistent results. I posted that most recent picture on the Facebook Clay Buddys group and have close to 500 likes and tons of compliments. Of course, nobody has asked me how much I want for them. hahaha
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Post by mohawkpiper on Oct 20, 2015 9:24:01 GMT -6
Not sure I want to take out the Li considering the heavy seeding that's there now. I prefer more ground than what I'm getting with that glaze, Hi Morgan, Reducing the zinc at least a few percent will help with this. I think maybe Arnie was suggesting the new glaze is too thin, not too thick.... Though I could be wrong. Sometimes the addition of lithium promotes seeding, not removes it, so in removing it you may get fewer crystals. (Because it thins out the glaze, and some glazes seed more when thinner.) It all depends on the glaze and whatnot. So this picture here...... This didnt change much in the strike. At least it doesn't look like it. Do you have larger sized images? When it doesnt change in the strike, and it has the right ingredients in the right amounts, that shows that the glaze is too thin. The thinner areas do not change, or if they do it is very very slight. Im talking strictly background here. More questions.... 1. Did you perhaps get new materials since the yellower ones that you are using in the newest iterations? if yes possibly new materials doing different things. If no then dont worry about this question haha. 2. Just to be clear and make sure i understand this right, you did mix up new batches of the glaze in the new iterations is this correct? Lithium is a strong one with a very small amount of material. it is difficult to measure it precisely and have it work the same way each time even with a scale that goes to .01 grams. It could be that perhaps you are measuring more of it and not being able to tell. Personally I try to stay away from lithium IF possible. Also, the "evolved pre and post strike" look like they have more iron in them than the "yellow pre and post strike". (as well as looking thinner.) The "yellow pre and post strike" look like it has more iron in it than the "nice yellow pre and post". You don't have a whole lot of ground and the pics are small so again it is hard to tell. G
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Post by mohawkpiper on Oct 20, 2015 9:35:40 GMT -6
Going back over the pics a second here... larger pics would be awesome if you can put them up...
But the second pot looks like a THICKER end thickness than the first pot. You see some of the color of the first pot in just the neck of the second pot. So overall second pot may be thicker than first pot.
Third pot looks like it has a THINNER end thickness than the first pot. the very top part of the rim of the first pot looks like most of the third pot.
many glazes have three or even four or more color ranges with exactly the same glaze (im not talking about mixing a new batch) they can achieve just by applying different thicknesses or more importantly firing to different melts.
If you are applying glaze as consistently as possible, and firing to the same cone bend, and this is in fact a thickness inconsistency I would point the finger to the lithium causing those different melts for you.
G
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Post by tileman2 on Oct 20, 2015 17:21:17 GMT -6
Greg:
Lithium is the one flux that can lose a fair amount of potency in a short period. Fresh [new] lithium is 11.0 PH, and can drop to 10.0 PH in six months if left out in the heat and stored in plastic containers. I know potters do not think in terms of PH; but a refresher to help all understand potency. A PH of 11 is one hundred times more potent than a PH of 10.0. So just losing .50 PH will change fluidity; which can occur in a short period. It is also effected by exposure to air- meaning do not let is sit around in unsealed containers. Best to store lithium in glass by the way. More reasons to look at lithium as being a possible suspect.
Tom
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morgan
New Member
Darn...lot of good info on the old forum. Sad that it got unstable. But whadya do?
Posts: 21
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Post by morgan on Nov 12, 2015 6:31:46 GMT -6
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morgan
New Member
Darn...lot of good info on the old forum. Sad that it got unstable. But whadya do?
Posts: 21
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Post by morgan on Nov 12, 2015 6:41:26 GMT -6
Larger pics of "old yeller" pre- and post- strike.
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morgan
New Member
Darn...lot of good info on the old forum. Sad that it got unstable. But whadya do?
Posts: 21
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Post by morgan on Nov 12, 2015 6:44:31 GMT -6
...and another pre- and post- strike. Need to do a bit more tweaking on this picture (too blue) but... the pot has sold so doubt I'll bother.
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Post by mohawkpiper on Nov 12, 2015 11:56:11 GMT -6
Hi Morgan,
Thanks for the larger pictures! They really do help!
Looking at that thickness test....
I really believe the entire thing is too thin. As you found, adding more coats isn't going to be the solution. It is fluxed too much that extra coats don't make a difference. It is in either the peak temp or the chemistry of the glaze. It is too runny (not to grow crystals and not for a crytalline glaze) but for extra applied coats to do anything visual.
I suggest you need to thicken the glaze up at the time the crystals are growing. I have tested with iron a lot and for me I get that look on your blue tape test piece when the glaze is fluxed out too much, or when the glaze sits for too long. (still not sure why it does that for a glaze that sits too long...)
Maybe if you have the time and piece(s) to afford another test, do one with and without your lithium (maybe backing off the zinc a little bit equally in both to ensure that you will have ground to see.) See what happens?
G
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