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Glass suckers

Posted: Mon Jan 27, 2014 7:09 pm
by Rachel K
I am having a problem with the glass contacting and deforming the surface in areas. I read on Bullseye to hold art 1250 for an hour when dropping to anneal tempurature but it did not work. Any suggestions?

Re: Glass suckers

Posted: Tue Jan 28, 2014 10:25 am
by Bert Weiss
There has been extensive discussion about suckers. Search the archives for posts by Glassburl. He was harassed off this board, so we no longer have the benefit of his voluminous casting experience.

Re: Glass suckers

Posted: Tue Jan 28, 2014 1:11 pm
by Kevin Midgley
you mean this post by him that is no longer on the board, lost in one of the backup failures?
I did not save the whole ten pages of posts at the time, only this part.
Rachel, the real answer is to use lead crystal.

I was asked by several Warm Glass members through private emails why I wasn’t revealing the “super-secret method” for applying my investment shell that I kept bringing up in this thread. It seemed a little “weird” to them. I was just “bragging” about it and not sharing with the other Warm Glass members. 

I wasn’t hiding my “super-secret” method, its not a simple method and I didn’t think most would be that interested. I was really trying to make the point that certain problems with investment casting could be dealt with if they were analyzed properly. (please see the other post "Uneven Heating and Cooling Problems ........,). 

My braggadocios comments that I was getting really good castings was to make the point, “Don’t put up with these problems! They can be solved!” Nevertheless, some were “offended”. That’s good. A true seeker is not so easily put off. That’s who shall be rewarded. 

And here at the end of this huge thread, tucked away in the far reaches of this corner of the internet for just a few to read, I will reward the very curious with “my” method.. I don’t intend to teach it, go on tour or anything else, except to try and continue to improve it to make outrageous glass castings more easily. So read on, curious ones, its all you’re ever going to get from me. 

I don’t expect anybody else to try this method. Its my method and I don’t doubt it falls in the category of “personal flatulence”. Nobody minds their own odor, but that same odor by somebody else is unacceptable! This is my method. I think its great! Just like you think your methods are great. No doubt you will find many complaints about its special odor that I have come to love. 

As I’ve followed where the solutions to numerous casting problems has led me, this is where I’m at, for now. I’m not asking for anybody’s “help” or “thoughts”. I’ve tried many different refractory materials that didn’t work out. If you have an honest question I may answer it. 

My method starts with two converted “mud” guns, the kind for applying texture to walls and ceilings. These converted guns are what I use to “blow” on the various recipes of investment and fiberglass shorts. I needed a metal lathe to convert these mud guns. These mud guns need an air compressor. I use three different configurations of fiberglass, four different mixtures of investment, three different proportions of water to investment and R&R 910 and FGR 1000, a slow setting gypsum concrete made to work with fiberglass. 

The first coat of R&R 910 on the wax design is a heavy mix, 30 parts water to 100 parts 910. Just as soon as this first coat is setting up I blow on a slightly wetter coat. Its at 1 part water to 3 parts 910. I blow on this same mix for 6 to 8 coats depending on the design. After the last coat of 910, I blow on the first coating of 1/4" fiberglass shorts. This is loose fiberglass, many use it in their investment mixes for greater strength and vapor paths. 

After this last coat of 910 and fiberglass shorts starts setting up, two more coats of 910 plus 10% by weight FGR is applied. The addition of FGR is going to make the 910 just a bit harder. After the two 10% coats of FGR and 910, then a coating of fiberglass shorts, then a 20% FGR and 910 coat, another coating of fiberglass shorts, a 20% FGR and 910 coat, a coating of fiberglass shorts followed by two coats of 30% FGR and 910. The fiberglass shorts adds some overall strength and thickness to this shell. 

The outside of all these coats is very hard (for investment) and gets gradually softer as you move towards the wax (thats the 6-8 coats of straight 910). Depending on the size of the wax this will take me 3 to 4 hours. This is the inner coat. It’s a very stable mix. It doesn’t heat warp. Lots of investment shell mixes will move when heated up and held for long at high temps. This mix doesn’t. I tested them all. Time consuming. 

After this inner coat is set up good, the outer shell is applied. I can even apply the outer shell the next day if I want. There doesn’t need to be any “adhesion” between the inner and outer shells. But the outer shell is necessary in order to keep the glass from bursting through the inner shell during the process temp. 

The outer shell is two parts. First I apply two layers of pre-cut 6 oz. fiberglass cloth with the straight FGR 1000. The FGR is made to work with fiberglass and has a working time of about an hour, depending on the weather. It has some adhesion, much more than just investment and goes on vertically very easily, and with a little work can go underneath forms, like the bottom of a vase form, and hold well. This fiberglass cloth is like the refractory material with the pure FGR gypsum concrete that keeps it from cracking. 

The 6 oz cloth is very conformable and fits the outside of the inner shell very tight. As I said, I put two layers of this cloth at the same time. I let it set up a bit and then apply the last layer of 1 ½ oz fiberglass mat. It is very strong but not as conformable as the 6 oz cloth. I don’t split this mat, just have cut it to make the biggest pieces I can that will fit the design. Sometimes big strips, sometimes little pieces. These sections of mat are overlapped carefully. When the FGR sets up, the outside of this shell is really hard. You could drop it and not hurt it much. Its about 3/8" to ½" thick with both inner and outer shell. 

You can’t use this outer shell method on the inside of vessel forms, the glass will crack when it cools, but I do use the inner investment shell method ,up to a point, on the inside of vessels. 

As stated many times during this long thread, I get really good castings with this method. You don’t get flashing to speak of, maybe something that can literally be brushed away with your thumb. The amount of cold working is almost nil, so I don’t mind taking the time to apply this method. There are no trapped air bubbles to clean up, really complex designs and detail come out perfect. The investment shell is breathable, the glass will push air ahead of itself and through the heated shell. I don’t use air escape sprues except for extreme designs, and maybe they are not necessary, but I can’t test everything. And there isn't a lot of mass to heat up, I can go up and down in temperature relatively quickly for casting. 

So what was the point of this mind-numbing detail about some arcane process that no one else will use? Was it really to reward the curious? No! I lied. 

It ticked me off when someone came up with the accepted party line about how “sharing enriches us all” or some line like that. Sometimes you just have to trust somebody else besides yourself, and this long explanation is the reason I knew I didn’t need to “share”my tedious "super secret" method! 

Plus just reading about it doesn't mean you can do it. It takes some practice. And like I said, no flashing or "fins" with this method. But if you screw up, major glass puddle in the bottom of your kiln. (yes, I've had several 20-30 lb leaded crystal failures all on the kiln floor. How much failure can you take?) 

But the vastly more important reason was to see if this thread could go 10 pages. 

Re: Glass suckers

Posted: Tue Jan 28, 2014 3:20 pm
by Rachel K
Thank you for digging that post up!
I think I will have to rewrite it in note form to process it.
I didn't know about mold deformation... I always thought it was the glass contracting.
Has anyone else tried his method?
Has any tried lead vs bullseye?
I do know lead always has beautiful results, melts a lower temp, and puts less stress on the mold.

Re: Glass suckers

Posted: Tue Jan 28, 2014 7:16 pm
by Morganica
The official story on "suckies" is that they form where the glass is hottest (whether because there's a bigger mass, or because the mold is superinsulating that that point). The idea is that the cooler surrounding glass is still contracting, but stiff, and so the contraction takes place where the glass is still very plastic. Because the plastic area is small, the contraction is proportionally more than it would be had it spread across the entire surface, so you get what looks like a weird air bubble in that spot.

I've seen indentations in the glass where, logically, that wasn't the hottest point, so I don't know that this is true in all cases. (and therefore the solution--adding a "sucker hold"--may not always work). Lead crystal is one solution--it's a dream glass to cast with (and coldwork), it's absolutely brilliant in transparent or pate de verre work, and I've never had an issue with suckies when casting with it.* It's not as stiff as soda-lime, and it flows better, so possibly it's simply less likely to stiffen up early in the cooling.

Bullseye took one approach to solving the problem--they added in a hold to slow down the cooling and help the glass cool evenly. I took another, because even though the sucker hold is not not SUPPOSED to be in the "devit zone" I do see more devit in those castings, and the suckies still sometimes happen.

I noticed that I never get suckies in open-faced castings, so I instead engineer the mold to be as open as possible when I'm using soda lime; I try to make the reservoir opening at least as wide as the footprint of the mold. Failing that, I underinsulate in thick areas and overinsulate in thin, to try and equalize heat loss when cooling. I may switch to a more permeable mold mix, such as hydroperm, or something extremely strong and thin, such as Hugh's mix. The closer the interior of the mold can get to the kiln temp, the more control you have over cooldown. I may also reorient the piece in the mold.

*That said, lead crystal is also a lot heavier, which can be an issue in larger pieces or in jewelry. It's far less likely to come in the color or form needed (good luck wanting powder or fine frit--you'll be grinding it yourself, and dealing with the lead dust), and if you're planning to sell it in someplace like California, which has serious lead restrictions, you'll have to go to some expense to have it tested and certified safe. So there are good reasons not to use it for some applications.

Re: Glass suckers

Posted: Tue Jan 28, 2014 7:19 pm
by Rick Wilton
unfortunately we've lost a number of valuable posters and made others reluctant to publicly comment because of similar instances.

It does a huge disservice to the community.

Re: Glass suckers

Posted: Tue Jan 28, 2014 9:43 pm
by Bert Weiss
Thanks Kevin, that is quite a treatise. I am wondering what he means by FGR? What comes to mind is fiber glass resin. I doubt that is what it means though.

I saw a demo once by Australian glass caster, Helen Stokes. She lays up her molds with layers of fiberglass cloth dipped in refractory, twisted and placed on the mold, as she builds it up by hand. In the end, she has a very thin strong mold that yields complex castings. If I remember correctly, she uses glass in a flowerpot flowing in to the mold to make the casting.

At any rate, she has a different approach, also won by years of testing, problem solving, and observing.

Re: Glass suckers

Posted: Tue Jan 28, 2014 9:53 pm
by Rachel K
Thank you for your posts!

Do you have any suggestions with this mold? My oven is only 13 inches deep and I cast two at once.
Would you make the mold thicker? Or wrap it in fiber blanket?
I built in about 6 layers.
Plaster silica
Plaster silica fiberglass
Plaster silica four more layers

My end vents filled nicely. The area where the blade mets the handle had some air bubbles even though I had a vent there
I held it at temp for 6 hours and the last hour I raised It 10 degrees to 1570.

Re: Glass suckers

Posted: Tue Jan 28, 2014 10:03 pm
by Kevin Midgley
re-read it Bert. It will become clear.

Re: Glass suckers

Posted: Tue Jan 28, 2014 11:45 pm
by Morganica
Probably I'd rethink the engineering of the mold, especially if you're doing some coldwork to get to the final product.

Can you show where the dimples are occurring, relative to the that picture of the mold in the kiln?

Re: Glass suckers

Posted: Fri Jan 31, 2014 4:46 pm
by Brock
Bert Weiss wrote:There has been extensive discussion about suckers. Search the archives for posts by Glassburl. He was harassed off this board, so we no longer have the benefit of his voluminous casting experience.

Was he really? I recall a somewhat different scenario. In one of his posts he threatened to come to Vancouver and punch me in the face. I immediately sent him my address and never heard from him again. He wasn't harassed off this board, he ran away. I agree he has a lot of casting knowledge but he was one of the most condescending posters ever on this board. I don't miss him at all . . .

Re: Glass suckers

Posted: Sat Feb 01, 2014 2:31 am
by orittlandau
i miss Huge,
No body is perfect. He is a sensitive person and a wonderful artist and I learnt a lot from him.

I hope he is all right and continue to cast wonderful works.

Re: Glass suckers

Posted: Tue Feb 18, 2014 4:22 am
by lucho/lachezar/
Morganica wrote: Failing that, I underinsulate in thick areas and overinsulate in thin, to try and equalize heat loss when cooling. [/i]

I always pour my moulds around the model ending with a heavy solid block and never get suckies.

Re: Glass suckers

Posted: Tue Feb 18, 2014 12:55 pm
by Morganica
lucho/lachezar/ wrote:
Morganica wrote: Failing that, I underinsulate in thick areas and overinsulate in thin, to try and equalize heat loss when cooling. [/i]

I always pour my moulds around the model ending with a heavy solid block and never get suckies.

What kinds of glass are you using? And are the molds open or closed?

Re: Glass suckers

Posted: Tue Feb 18, 2014 1:40 pm
by beninfl
I will happily come to Vancouver and punch you in the face if you'll trade that service for glass training! :) :) :) :) :) :) :) :)

Re: Glass suckers

Posted: Sun Feb 23, 2014 12:27 am
by twin vision glass
I had some really great success with different kinds of mold material that could breath and lots of vents and venting right to the top of the mold to get all air out but mostly by holding the mold at 50 degrees lower than slump temp (around 1180 F. if I remember correctly ) for 2 to 8 hours or more and then continue down to anneal. Just to let everything equal out and the inside temp to catch up to the outside so there is no shrinkage and pulling away from the mold which caused suckers. I really liked the discussions on the board with Hugh and really like what he had acheived in kiln casting which has been hard to duplicate.
http://www.twinvision.fusedglassartists ... dles10.jpg I was getting no suckers or concaves at all and no bubbles either with the right molds and well., I miss casting sometimes. I am doing more colour bar work but still love to see what artists are achieving. Richard Whiteley and Clifford Rainey are two of my favorite casting artists as well as Hugh. Les
http://www.twinvision.fusedglassartists ... ld004.html Oh my , here is a mold out of Mold Mix 6 with many vents . Goodness. But mold mix 6 definately breaths but if put on tooo thick it is not good for sharp shapes. Great for soft sensual shapes though.
http://www.twinvision.fusedglassartists ... 010560.jpg
http://www.twinvision.fusedglassartists ... an0002.jpg
Over kill on vents BUT mold mix 6 is a different beast and this actually was a structural overkill so that it would help support the Gaffer crystal I had to use. It is very tall and well it needed support and this worked well for not only the glass but the bronze piece too. Les