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Old 01-21-2021, 09:24 AM
Josh Bernbaum Josh Bernbaum is online now
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Small stones, UGH..

Having issues with tiny stones throughout my last 3 melts. Don't know what options I have left to try to get rid of these. Here's my info so far: Been melting SP batch (standard pelletized 87 w/Er) exclusively in the same 200# moly for 10.5 years. Largely pretty good glass over that time, even renters have mentioned that too so it's not just my take on that. Have seen occasional stones in gathers over the years but few and far between. Crown was replaced approx. 4 years ago if memory serves correct. Looked in decent shape to me when I took it off to change the pot this past fall, with only some hairline cracks that I noticed. But no 'spalling' as I've heard it called. Pot that's in there now, one of Pete's (I've only ever used these ones and have no other complaints about them), is only 4 melts old now. What's interesting to me and worth mentioning is that I didn't see any stones in the first of those 4 melts. Just in the past 3, with the worst result being in melt #2. These are small flecks, I've seen larger stones in the past like in colors I've made where I didn't sift the alumina hydrate adequately. But these small stones are around the size of a grain of cream of wheat cereal, and the same color (whiteish) if anyone is familiar with that breakfast option. I've been scooping out as much of the heel at the bottom of this round-bottom pot as I can before the last 2 melts, to see if I could get all offending material out before new batch went in. No cullet was mixed in either, just batch. Two separate batch runs from SP that I've charged throughout these last 4 melts, but stones seen with use of both batch runs, so I think I can rule out the batch? All melt times, temps, process, everything else the same as what I've done for years with this furnace. Glass viscosity feels like what I'm used to, and glass is cord and striae free, and mostly bubble free otherwise as far as I can tell. One more thing to mention is that I did have to change one element hot after getting up to temp originally, but before the first of the 4 melts. But if there were any material that went down through that hole in the crown during that process, I figure I would have noticed it on melt #1 but that has been my only clean melt so far with this new pot. I did see some flecks of material on the top of the rim of the pot after initial heat up (and before hot element-swap), which can still be seen a bit now, which I think is some flecks off the surface of the elements because it's right under one or two of them. I just don't know what to try next. And it's not even 2020 anymore so I can't blame the issues on that.. Sorry for the long post, I don't know how to explain anything quickly. Any recommendations on what to consider next?
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Old 01-21-2021, 09:52 AM
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I would be most suspicious of it coming down from the crown and those element holes would be where I'd look first.
If it was me, I'd try turning the melt temp down 25F or I'd try a much colder melt at 2175F with smaller charges.

It does not sound like either the pot or the batch although earlier melts of other formulations could possibly affect that.

I'd order a crown if you don't have a spare.
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Old 01-21-2021, 11:16 AM
Josh Bernbaum Josh Bernbaum is online now
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Thanks Pete. On the recommendation of lowering melt temp, is that more for the temp I charge at (2275) or my "cook" temp afterward (2300), or both? I can't get away with 2175 if I'm filling the pot, because it would just take too long with this (non-gas) furnace. But I suppose I could try a half melt at those low temps at some point.

Perhaps I'll order a spare crown, but I don't know how much longer I'll be keeping this furnace. My thinking was keeping it for at least the life of this latest pot I put in. One different thing that's maybe worth noting is that I am noticing this 'indentation' about halfway down the inside wall of the pot, maybe about 1/2 inch wide that rings around the pot at that level. It's hard to see at my gathering temps but more noticeable when I'm looking in there while charging at the higher temp. And please don't construe this as me trying to place any blame on the crucible manufacturer, but it is one other difference I haven't seen before and wondering if that could be contributing? But then again, I've seen stone-free glass come out of old pots that looked like swiss cheese..
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Old 01-21-2021, 11:37 AM
Chris Lowry Chris Lowry is offline
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Of course you would be suspicious of the crown or changing the element. Although from my experience if something fell in you would see the evidence and then after scooping and cleaning it would go away.

Next question is batch, is this the same batch run you were using before? Are you trying different runs?

Years ago we had the same issue of stones in a new crucible. Of course it had to be something else. Spent months changing crown, elements, charging schedules... finally changed crucible and all stones went away. I know Pete hates hearing it but sometimes the crucibles just go bad. We have also had a much shorter life on our crucibles for the last three than previously crucibles.

I would clean the crucible like crazy, do the same melt as always and see what you get. If stones are all the way threw the glass and not just floating on top, Iíd change the crucible.

On another note our crown now looks like hell. Looks like it would fall apart any day, but Iíve never seen a stone except the day before the crucible popped a hole.
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Old 01-21-2021, 03:39 PM
Josh Bernbaum Josh Bernbaum is online now
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Quote:
Originally Posted by Chris Lowry View Post
Next question is batch, is this the same batch run you were using before? Are you trying different runs?

I would clean the crucible like crazy, do the same melt as always and see what you get. If stones are all the way threw the glass and not just floating on top, Iíd change the crucible.
Thanks Chris. About the batch, the first 2 melts in this new pot were the last bags of a production run from SP that I had melted in the previous pot (with no stone issues). And in these last 2 melts with this new pot I have been charging bags from a recent production run of theirs. So it does seem that I should be able to rule out the batch as a culprit, especially because SP have been so consistent in my experience.

For the crucible change, I just don't know if I can come to terms with that if that is the culprit. All this shit is so expensive these days, it's like a thousand bucks including freight fore this size pot and I would have trouble being okay with only getting a handful of melts after spending that much money.
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Old 01-21-2021, 03:55 PM
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If the bags of batch haven't changed , then it's unlikely to be the source. If they have changed, it's far more likely. You describe a ( in your words) tiny stone that doesn't seem to melt . That suggests alumina to me if it is not melting anywhere but at the same time if the stones are throughout the pot, I consider it unlikely that the crown is just sprinkling fairy dust on your melt constantly.

It could be the pot, it's always possible. We are half art/half science and always have been. We turn them over to people who periodically do unexpected things with them. I have seen on many occasions where the batch being melted in the pot gets switched to something else and the pot appears to have six months wear on it overnight. Particularly true with barium containing glasses changing to boron glasses. That can make a pot look like roughly screed concrete overnight. Tiny little stones that all appear at certain temperatures and not at others.

Lowering the melt temp may be inconvenient but it's part of a seining process to find the problem. It needs to happen if you choose to be analytical. Chris suggests our pots are just no longer up to snuff but I don't hear that as a regular complaint. If I did, It would be actionable. Far more likely that some process is changing in the studio that is not getting noticed. I take note that lots of people think it's just time that wears a pot. It's the frequency of charges of a specific viscosity glass at specified temperatures over time that wears them out. Or turning them on and off. They are not meant to be a permanent fixture. The fact that they are replaceable is the entire point in their existence.

So, again, I'd turn it down, do a smaller batch, let it run longer. See if you get stones. If you don't you're learning something. If you do, you're learning as well. You could load with a cullet, now you're learning again. Blah blah blah..
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Old 01-21-2021, 06:45 PM
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All things being equal, it really has to be something that changed.

You changed the pot, and you also changed the batch (new lot#).

I had stones like that on a couple of occasions, and it ended up both times being a batch change.

However, what I found is that it takes about 5 melts after the batch change, then the issue goes away for as long as you are using the 'new' batch.

So my immediate advice would be to do a few more melts exactly the same way you always do. If the problem persists after that, then it's something else, but I'd go for a few more 'normal' melts before you do anything else.

Or you can do the half melt at lower temp to see what happens, but if I'm right you won't see any change in the tiny stones. I tried turning up, turning down and so on, but in the end it was 5 or so melts that did the trick.

It's as if the glass sticking to the pot doesn't like the batch change and just reacts this way until you've replace it all, which (again) in my experience takes about 5 melts. It might take a few more in the bigger pot.
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Old 01-21-2021, 07:04 PM
Josh Bernbaum Josh Bernbaum is online now
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Quote:
Originally Posted by Richard Huntrods View Post
You changed the pot, and you also changed the batch (new lot#).
Thanks Richard. I did change to a new lot/mix # of Spruce Pine, yes. Say lot A was the first pallet I finished and lot B is the new one I recently started. But in my previous pot, before changing pots to this new one, I melted lot A for months and months. Then after changing pots, used the last 6 or 7 bags at the bottom of the pallet of lot A. Stones seen in the second of those two melts in this new pot, but not the first. Then for melt #3 and #4 in this new pot I used the first bags of lot B. Still stones detected, however melt #2 (last bags from lot A) has been the worst so far.

I'll keep scooping out the dregs and see if I can get a half melt in with the lower temps sometime soon.
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Old 01-21-2021, 11:56 PM
Chris Lowry Chris Lowry is offline
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I will say that over the 20 years we had the studio we have had all sorts of issues, Iím not an expert I can only relay my experience.

We also had a time when using Phillips batch that we started having stones and nothing seemed to solve the issue. We switched to Spruce Pine and stopped having stone issues. It for sure could be the batch but how you used the new batches doesnít sound likely. You could always buy new batch and see what happens.

I still think crucible or batch... you might be able to wear away the bad part of the crucible and get back to no stones, like Richard suggested. 🤷‍♂️

I think Pete takes a very scientific approach to glass, itís what he seems to enjoy. I go by more of the empirical, trial and error.
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Old 01-22-2021, 08:11 AM
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I think Pete takes a very scientific approach to glass, itís what he seems to enjoy. I go by more of the empirical, trial and error.
****
And you are the kind of guy who calls in the middle of the night, totally lost.
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Old 01-22-2021, 10:38 AM
Chris Lowry Chris Lowry is offline
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True, Iíve done it before.
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Old 01-22-2021, 02:30 PM
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Always debug one variable at a time. 30+ years in software has driven that in to my brain forever.
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Old 01-22-2021, 03:51 PM
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Josh, are the stones flat or rounded? Are they white? Well in focus? What frequency are they seen in? Is it throughout the melt, bottom to top?
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Old 01-22-2021, 03:53 PM
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Quote:
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Always debug one variable at a time. 30+ years in software has driven that in to my brain forever.
**********
This.

Except of course when you have a perfect storm of three variables all interacting which I regrettably see more than I care to.
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Old 01-22-2021, 06:23 PM
Josh Bernbaum Josh Bernbaum is online now
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Quote:
Originally Posted by Pete VanderLaan View Post
Josh, are the stones flat or rounded? Are they white? Well in focus? What frequency are they seen in? Is it throughout the melt, bottom to top?
Not flat, but I've seen those occasionally over the years though. I suppose more rounded I'd say. And very small for the most part. They are throughout the melts. I think I had the cleanest of my last three melts this current pot-fill, but still saw them here and there in most gathers. When I've seen small bubbles in my melts, I usually don't tend to see them until the larger gathers. But with these small stones, I have seen them even in tiny gathers. We use a rake religiously here before most gathers (for years now), but it's not seeming to help. Or maybe it is helping somewhat, but not helping completely, I don't know. I took some fairly clean larger gathers today at around the 1/3-1/2 full pot level. But then the gathers after that showed some of these little stones again.
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Old 01-23-2021, 01:34 AM
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Josh, I would tend to agree with Pete that it may be alumina, but let's back track a minute. You said the two changes were a new batch lot, and a new element install. I'm suggesting you look at the second item a bit more. A new element can run hotter or colder than the others and the temperature difference not picked up by the monitoring/controller system you are using. If you didn't check the draw on each leg, you would never know. With electrics, there is not the same convection/mixing you get with gas fired. I would empty the pot, run the furnace up to sintering temp for the same holding time you would use for a new pot, and then back down to charging temp, or maybe a bit lower and let the furnace rest for a couple of hours before charging as usual.
That's just my 2 cents, by now you may have found the gremlin. Good luck and let us know what you find!
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Old 01-23-2021, 09:56 AM
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at this point, I think it's the older batch that you switched. In humidify that the northeast experience, batch clumps in funny ways. Since it's throughout I doubt very much that it' s either the pot or the crown.

Either mix up a batch of a good 96 ( mine would do) or get a fresh ag of SP. If it is the batch, turning it up, not down, for longer would be my approach.
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Old 01-23-2021, 10:38 AM
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Well I do have fresh bags of SP now. Just got a shipment a few weeks ago that was mixed in NC with the date on the bags being December 2020. The last two charges I've done have been exclusively this newer batch mix. I certainly want to avoid throwing any other type of batch in there at this point, because I know that will come with it's own set of issues that we tend to see when changing types of glasses from melt to melt in the same pot. I'll try another 25 degrees to 2325F, and another hour 'cook' I suppose. I'm debating whether to not potato this next melt too, like I have done religiously now for years.

And thanks Brian for the input. I have never 'sintered' a new pot. I thought the fuse-casting at the high temps when they are made at the factory handled that curing process? One other thing that I think is still curious is that the first charge in this new pot rendered clean glass (besides some striae I saw making some thin ware). But no stones detected until that second melt. Again, both melts #1 and #2 in this new pot were done with the last bags of SP on a pallet I had been melting for months and months with my previous crucible (with no stone issues), just before getting this new shipment of batch.
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Last edited by Josh Bernbaum; 01-23-2021 at 10:43 AM.
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Old 02-05-2021, 02:05 PM
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So, Josh,

What has been the outcome on the stones?
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Old 02-05-2021, 04:47 PM
Josh Bernbaum Josh Bernbaum is online now
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Sorry haven't posted any updates on this since, but thanks for checking in Pete.

I've done one more melt since last posting about this. What I did differently was increase the temp from 2300 to 2325, and added another hour to that "cook" time. I also did not potato for the first time in years, just to see if a lack of stirring would keep any flecks from spreading around. Glass was okay I suppose, but I'm still seeing some of these really small white specks in the current melt.

One thing I noticed in scooping out as much as I could with a ladle before this latest melt, is that I didn't seem to notice the specks floating in the ladle with each scoop. Until, that is, when I tried to 'scrape' the dregs out of the bottom. Those small scrapings that I pulled out with the ladle had many, many fine glowing-red specks. But when I see these things in my gathers they look like tiny white specks, even fresh out of the furnace. I don't think I'm getting everything out with the ladle.. Maybe I should 'swab' the bottom/sides of the pot by making a makeshift gathering ball on the end of a clogged pipe?

My thought to try for my next melt on Monday has been to NOT scoop any out (it's mostly empty, there's maybe 3-4" of depth in there currently), and charge on top with fresh batch. And then NOT potato. I suppose my thinking is to see if the dregs will stay down there or not. I don't think I have a lot of convection in my small(ish) 22" pot in an electric furnace. But I just sort of wanted to see what will happen with that methodology before trying to swab the pot by gathering the dregs versus ladling.

One more thing to mention about the batch is that I have now seen these offending particles in my melts in 3 separate lots of batch from SP. Perhaps these stones originally came from one bag, charged months ago, and I just haven't gotten it all out yet. But I don't think more of them are coming from these newer bags of batch I have. One mix date from SP was December 2020, and another is Jan 2021, so it hasn't been sitting around for that long.
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Old 02-05-2021, 06:11 PM
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I don't think dragging the pot wall clean helps at all. Getting the bottom glass out is the point.
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Old 02-06-2021, 03:47 AM
David Hopman David Hopman is offline
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Weld a 4-5" by 2" by 1/4" bar of steel to the end of a punty for a good scraper. Grind a curve in it to match the profile of the bottom of your pot if not flat.
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Old 02-06-2021, 08:50 AM
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Don't scrape your pot. The potato will get what needs to come off handily.
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Old 02-08-2021, 12:34 PM
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ive had similar situations with shit in the pot. Stainless nuts, ceramic ferros, chunks of castable. <-public studios

when it came to scraping the pot clean, i found a glass rake (afro called em angel wings) got me the cleanest result. im assuming you know what it is, but for those that dont, its a flattened gather, spun out in a rake shape (sorta like exaggerated ballotini post). can just keep cutting of hot glass to keep a useable size. should be able to get most eveything out the bottom.

i dunno. may be useful, maybe not. good luck.

Last edited by Michael Hayes; 02-09-2021 at 01:10 PM.
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Old 02-13-2021, 01:25 PM
Chris Lowry Chris Lowry is offline
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Still getting stones? Change the pot yet?
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