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Steve Lazer 05-09-2020 07:25 PM

Kiln casting
 
First off I hope all are well safe and remaining sane in this time of lockdown. I have a few questions on kiln casting, something I can do without studio access.

In creating a plaster mold I know Pete mentioned adding alumina to the plaster mold for increased strength. My first question is what type of alumina - tabular or carbonate or ....?

I will be looking at bomma cullet to cast with and am looking for additional guidance on kiln schedule for a very thick piece 8 inches in one dimension.

Thank you
Stay safe

Steve

Pete VanderLaan 05-10-2020 08:03 AM

If you can, get a copy of "The Schedules" By Graham Stone. Brad Walker has itt usually at the warm glass board. LIFE'S WORK ANALYZING ANNEALING SCHEDULES FOR CASTINGS.

Roseanna recommended hydrated alumina if one was to add it. There's a lot of ways to go after the mold work and Glassnotes IV covers many of them. We got hijacked in our approaching the molds by COVID 19 and haven't been in the studio at all. There are some great videos on the subject on youtube.

I do tend to think the issue many of us would like to solve is reusable molds. That's why I was leaning to the alumina.

Shawn Everette 05-10-2020 11:26 AM

The standard one time use is silica and plaster, I've used other silicates like diatomaceous earth with some success.

The best success boost has come from being able to back up a mold with a "container". Either by pouring your mold in a steel box or can, or banding thin sheet around it.

I haven't cast with the bomma yet, but most of the time with cullet you will end up seeing the ghost of every piece. You can sometimes get around it if you do the flower pot method.

Eben Horton 05-10-2020 12:44 PM

I used to have great success with using dental investment plaster to form a 1 to 2 inch skin around my wax and then made a 50/50 plaster silica mix that I reinforced with stainless pins that are sold as a refractory reinforcement. In my opinion the steam release of a wet mold will give you flashing problems more than what material you use so take that into consideration

Pete VanderLaan 05-10-2020 02:02 PM

Quote:

Originally Posted by Shawn Everette (Post 147730)
The standard one time use is silica and plaster, I've used other silicates like diatomaceous earth with some success.

The best success boost has come from being able to back up a mold with a "container". Either by pouring your mold in a steel box or can, or banding thin sheet around it.

I haven't cast with the bomma yet, but most of the time with cullet you will end up seeing the ghost of every piece. You can sometimes get around it if you do the flower pot method.

****
"The ghost of every piece" Indeed. I remember when Gary Beecham was pulling cane at Pilchuck back in '76 and he kept 8 inch diameter PVC tubes that had caps for both ends. As fast as a cane was pulled, it went into a tube until it would be used. Cullet collects dust in the very process of being removed on a rack from the furnace and as Dan Fenton used to say ( RIP Dan) "Glass remembers everything you ever do to it."

Rick Wilton 05-10-2020 04:10 PM

before you get too far committed, test the bomma cullet out first.

I took a few handfuls of the bomma cullet and threw them in a simple fiber board square mold to see how that would go. Mine came out a devitrified, cordy looking mess.

I suspect that the glass needs furnace temps for a full melt first.

Admittedly, mine was a one off attempt but I can get good clear castings from cristallica that has been through the furnace already.

Pete VanderLaan 05-10-2020 04:28 PM

Bomma was intended to be very close to SP87 as a glass and SP87 is well known for devitrifying as a casting glass. SP has barium in it which doesn't bode well for being a weaker glass structurally. It does brighten soda glasses.
I'd like to hear more about it going south.

Greg Vriethoff 05-10-2020 06:22 PM

The great challenge in kiln casting with soda lime glass is dealing with devit. It's a "perfect storm" scenario where the temperatures that are ideal for flow are at or above the temps. that plaster begins to breakdown. This is just one reason lead crystal (like Gaffer) are easier to work with (lower flow temps.).

You'll have nothing but heartache with any of the boutique cullets. The other factor is that the temps. that you want are also where devit. is most likely to form (~1,500F).

No. 1 pottery plaster and ground silica (flour) are the basic ingredients. I have used a recipe that involves EPK kaolin. The jury's still out on that one as I have not tried it enough to note any difference. It's also a recipe that I obtained from someone else, so I won't share it here since I have not asked permission.

I highly recommend you avoid introducing metal of any kind into your process. When I was learning we did the chicken wire collar that many like. I have a colleague that has since told me to ditch the chicken wire, and I get better results. The one additive I highly recommend is chopped fiberglass. It's easy to obtain.

Seriously, get lead crystal to cast with. If you must cast with soda lime, use Bullseye. The stuff formulated for blowing is not engineered to be worked at the temps. for casting regardless of how it is advertised.

Reusable molds are a pipe dream.

Shawn Everette 05-10-2020 07:00 PM

I too used kaolin, but that didn't seem to perform any better than the silica. It seemed to change the viscosity of it too, and I wasn't as fond of it. Picking it out of your arm hair is the worst.

The head of the sculpture department thought silica was the devil (he hated glass grads too) so I was forced to experiment with a number of alternatives. Not that any of them were healthier for you. The diatamacious worked best, but you have to get the powdered version(home depot), kitty litter works for shit. In the end we went back to siica, just dumping it into unmarked containers, he rarely went to our department and couldn't tell silica from powdered sugar.

I agree on the fiberglass vs the metal. Had better results and the metal would stain the glass if it made contact with the glass.

With the metal container process you eliminate blowouts and there is no contact made with the glass.

I've been happy with bullseye from a devit standpoint, not the cleanest or colorless.

Pete VanderLaan 05-10-2020 07:08 PM

mine casts beautifully but it's not available as a cullet.

Greg Vriethoff 05-10-2020 10:11 PM

Speaking of Dan Fenton I have a copy of this book that has a number of recipes for investment. I haven't vetted much of the content with real-world experiences yet. I still don't have access to the proper equipment.

I also have this one. It's a good source for general knowledge of kiln work across the spectrum, but I have issues with some of the firing schedules.

The Graham Stone book is at the top of my list right now of needed acquisitions.

Pete VanderLaan 05-11-2020 08:59 AM

There is one copy for sale on Amazon.
https://www.amazon.com/Firing-Schedu.../dp/B002XPG2VQ

It's fifty bucks, up from the original price of $30 bucks. It will save anyone in kiln work a lot of grief.

I note that HIS Glassworks apparently sells it as well.

Eric Trulson 05-11-2020 12:24 PM

Yeah, seconding the Graham Stone book. It paid for itself within the first few months of me getting it. I have been nearly comatose in terms of glass work this past year, and I've still cracked it open two or three times to check on information that I just would not be able to find anywhere else.

The really nice thing about the book is that there are a ton of specific examples and schedules which you can just pull as-is and use directly, but he also goes into sufficient detail about his assumptions and thinking about the heat transfer process from the kiln to the glass. That way if you're dealing with a situation that isn't quite covered with an exact schedule, you're usually able to pull a few similiar schedules together and think through how to change things for your particular situation.

Pete VanderLaan 05-11-2020 01:13 PM

It really was his life's work and is remarkable when one considers what's actually in front of you in terms of testing.

Years back, Graham was a regular contributor here and at Brad Shute's site. I had written some material and actually no longer recall the contents but the material I wrote was lifted entirely by this guy named Mike Firth and put on his website and Brad demanded that he expunge it from his site. Firth refused saying "anything on the internet was public domain" which is not true. Ultimately he did take the material down.
Graham was absolutely shocked by the assertion and completely withdrew from any internet interactions. It has remained that way for years and I indeed do miss him.

Buy his book, don't copy it.

Shawn Everette 05-11-2020 05:35 PM

Firth's site is a hot mess of cut and paste, I'm not surprised he tried to pull some "public domain" nonsense. It never ceases to amaze me how many aholes there are out there that try and steal your work while pretending it was their idea. I see a few of those standard bearers regularly on the glassies page.

Eben Horton 05-13-2020 10:08 AM

I took a look at firthís website about a year ago. I see something like a digital studio notebook or something to help him learn the craft. Was he building that site for his own education? That is what I felt like when I saw it.

Pete VanderLaan 05-13-2020 06:47 PM

Firth signed up for a site ostensibly explaining how glass is dealt with world wide. He simply copied and pasted what he found regardless of source and did not give attribution for what he found.

He is an employee of a hardware store or was at the time. A hobby.

He signed up for a class with Fritz giving a self evaluation as " Advanced".
Fritz said he was a raw beginner after about ten years trying. .

That was a good ten years ago, perhaps more. I think of him more as a thief.

Joe Pfeifer 05-14-2020 12:55 AM

Firing Schedules for Glass
 
You can buy from Amazon, either listing is fine. ISBN 0578054957 The $50 listing is from the publisher, or you can buy from the website:

https://www.glassbookstore.com/produ...y-graham-stone

Other books there are Hellmers, Volf, Scientific Glassblowing, and Hot Glass Information Exchange. Tell me you saw this on CraftWEB and I will ship free (USA).

Pete VanderLaan 05-14-2020 07:56 AM

I really encourage supporting Joe's store on this. He has done a great job of bringing out of print material back. Volf was a great example. Also the hot Glass information exchange.

Greg Vriethoff 05-16-2020 01:39 PM

Quote:

Originally Posted by Pete VanderLaan (Post 147773)
He signed up for a class with Fritz giving a self evaluation as " Advanced". Fritz said he was a raw beginner after about ten years trying.

My experience has shown me most people overestimate their actual skill level. I got involved with all of this a little over twenty years ago, but I would estimate my own skills at the bench to be intermediate at best. Of that two decades I've been hands-on blowing less than a quarter of that time. There's a fair amount of cold working, casting, education, independent research, slave wages, etc. If I'd spent that two decades at the bench five days a week it'd be a different story.

I know my way around a shop and can hold my own if asked to assist. I would not label myself "advanced." Not ready to gaffe anyone else's designs.

Pete VanderLaan 05-16-2020 04:52 PM

Fritz is actually a very kind person. The evaluation was generous.

Steve Lazer 10-11-2020 03:37 PM

I have Grahmís book but am now looking for glass
 
Good afternoon all after a very tumultuous run through COVID that cost me my bride I am trying to return to some normalcy. I am looking for recommendations on glass for the kiln cast. Pete Iíd be happy to use your formula, but am still looking at a kiln cast. Any recommendations will be appreciated.

Thanks all.

Shawn Everette 10-11-2020 04:11 PM

My condolences Steve.

Schott crystal is really the go to clear, but it can be hard to come by anymore. Gaffer has some really nice colored billets, but sometimes has production availability issues. Bullseye's probably the cheapest "casting" glass, but will the more difficult to work with. I don't know anyone that's ever used Reichenbach, don't care for the pallet and OCR is still down so you can't even browse. I can't really recommend any "furnace" glass, has the wrong properties at the wrong temperatures.

Pete VanderLaan 10-11-2020 04:43 PM

Quote:

Originally Posted by Steve Lazer (Post 149054)
Good afternoon all after a very tumultuous run through COVID that cost me my bride I am trying to return to some normalcy. I am looking for recommendations on glass for the kiln cast. Pete Iíd be happy to use your formula, but am still looking at a kiln cast. Any recommendations will be appreciated.

Thanks all.

***
That is just so sad. I hate this man.

My friend Eveline wrote me today and maybe Wang Kai would sell cullet from our Shanghai shop. We knew it cost .04 lb to ship across the pacific as a container load and they could make the stuff. It' is my last formula which is still nice stuff. I have never talked to them about making the stuff I designed for Spruce Pine, which is a better glass period. But the devil is in the details.

Spruce Pine will mix it but I don't have anyone to melt it and make it into cullet besides Shanghai. I could melt it here in small quantities here but it would be costly to process and ship. . Maybe get someone up there to melt it.
Beautiful stuff.

I have a few tons of Schott in an LF 5 and an f2 some in slabs and some buckets full of drops. but it would have to be picked up here. Also a ton of an Neodymium pile of slabs. There's lots of other slab as well. I don't see us doing more with that.

Steven O'Day 10-11-2020 08:29 PM

I've had good results with Bullseye and Gaffer, and Spectrum when they were making it. I prefer Gaffer, it comes out of the mold cleaner and fires at a lower temp. Even after considering the different densities Gaffer is cheaper. It does look like Gaffer is out of billets though.


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