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devit issues - need help

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devit issues - need help

Postby library » Thu Apr 04, 2019 12:51 pm

I have been following the bullseye method for glass cleaning, mold making (2-layer), firing schedules, using, of course, bullseye glass billet.

My first question is:

1) my current glass works are made using the open face mold method show no signs of devitrification on the back surface (the surface open to the kiln), but the facing surface (the surface making contact with the mold) shows signs of devitrification. I'm not sure what else to do at this point since i am following bullseye instructions so rigorously. My only thoughts are:

- I am allowing my molds to air dry for too long (2-weeks)
-I am making my molds too thick (usually 3/4" for each layer)
- There might be ambient dust settling in my mold
- I should be using distilled water to make my molds
-my plaster/silica mixture is old
-The firing schedule for open face molds is not correct

Please find below pictures of a recent work in gray glass which shows devit, and another in green glass, following the same methods, showing no signs of devit. It seems to me, in looking at the gray glass work, that marks on the surface of the mold are causing this effect. Essentially i am just trying to eliminate problem areas. Thanks again for all the help!

Best,

Richard
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Green glass with no devit
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Re: devit issues - need help

Postby jestersbaubles » Sun Apr 07, 2019 7:01 am

Normally, devit occurs only on the air side of glass. I can't see the gray glass in the photo (only the large green piece in the middle), so I don't see what you are referring to, but my guess is what you are seeing is just a matter of the glass coming into contact with the surface of the mold. The mold side of the glass is always textured and duller than the air side. You can coldwork or fire polish to shine up the surface.

Dana W.
Dana Worley Fused Glass Designs
dba Jester's Baubles
http://www.jestersbaubles.com
http://www.jestersbaubles.blogspot.com
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Re: devit issues - need help

Postby jagboy69 » Wed Apr 10, 2019 11:42 pm

I think what you are seeing is something going on with the mold surface. What is your dewax/burnout method? I spent considerable time on the phone today with R&R for this exact issue. My case seems to be a bit more extreme. What kind of glass are you using too?
I've been trying it with 104 which I am learning isn't the correct stuff. Any attempt to fire polish that green piece will probably result in loss of detail on the coinage.

Anyone know anything about this "clear coat" that can be sprinkled on and refired to turn a surface clear???
thanks.
Jason
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Re: devit issues - need help

Postby library » Thu Apr 11, 2019 8:27 am

Jason/Dana,

I'm making my initial positives out of a number of materials. Sometimes I use wax, and steam the wax out per the bullseye method (wallpaper steamers). In other instances I am placing my investment material directly onto a clay or silicone positive, which avoids the steam-out method entirely. I'm using bullseye billet and mold making techniques for all projects. I have attached another work i recently pulled from the kiln, again showing signs of white reside upon the surface. The back face shows no signs of devit at all.

R
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Re: devit issues - need help

Postby library » Thu Apr 11, 2019 8:36 am

Additionally, here is a close up image of a different, entirely successful work with same firing schedule, glass cleaning, glass, and mold methods which came out without the white residue and is mostly clear. At this point the variables are confusing, mostly so because i have had success with varying materials of positive forms that i place investment upon to produce my investment mold.

The only thing i can think of is the plaster/silica mix might have "gone bad"...... Any sugesstions would be much appreciated.

And, again, i don't think i can fire polish these works as i will lost the fine detail. Last question, is there a spray that functions like the effect when the surface is wet, essentially eliminating the white scuzz on the surface?

R
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Re: devit issues - need help

Postby jagboy69 » Thu Apr 11, 2019 9:05 am

Wow! That's considered to be clear? I must be missing something here or my expectations are too high for this glass stuff... I'm new to casting glass, I'm a bronze caster trying to add cast glass pieces to my work. But hey, I'm probably more technical support than what you will get from other sources. lol.

R&R does only recommend to use distilled water due to unknown alkalinity in your tap water.
So yes, I would start with that. Next, the guy told me to watch how long you steam and not over steam the wax out. He said better to smoke your neighbors out burning the wax out than trying to steam all of it out of the mold. He also said when driving off the moisture to stay around 300-350f for 3-4hre and ramp molds slowly, not more than about 150f to 200f per hour. Something else I learned, He said this investment should only be fired once. So after burnout, load the glass into the hot mold. Do not cool back to room temp and refire. Some of this schedule might not jive with what the glass guys recommend for their glass. As of now, I have not been overly impressed with the level of knowledge from these glass companies or their people. Seems, since people quit smoking, casting ashtrays has gone out of vogue and knowledge has greatly suffered. Make beads and you'll find all sorts of help. Just not for casting. That's how I ended up with 104coe glass for my project. :-/ I will say this, as I am still not having success either, I will be going with gafferglass for my next attempts. They are now here in the US so no more NZ nightmare shipping. Here's a link for ya.http://www.gafferglassusa.com/index.php?route=product/category&path=88_61

Please do let me know how you make out. I'm in the same boat as you on this one. Maybe we can help each other out.
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Re: devit issues - need help

Postby library » Thu Apr 11, 2019 9:22 am

In terms of your "clear" question, the lack of clarity is due to the nature of the surface I pulled the mold from. It was quite 'bumpy' so that affects the optical quality of the glass, but yes, it is very clear for what can come out of a refractory mold :) I'll let you know if i learn anything - my next trial will be surfacing with a product called mold mix 6 (made by a company called Zircar), and then adding the usual plaster/silica mix on top. I have done a Zircar mold (not open faced like my usual reliefs) and the glass was incredibly clear. Here are some images, it is a two sided relief.

You can divest the Zircar mold using CLR or coca-cola :)
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Re: devit issues - need help

Postby jagboy69 » Thu Apr 11, 2019 11:06 am

Interesting... I'll be watching to see how it works out. Are you following my same issue with the blue chunk of glass? I'm going back in the kiln today and should know something tomorrow if my dewax/burnout changes helped. Stay tuned!
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Re: devit issues - need help

Postby marykaynitchie » Fri Apr 12, 2019 2:00 pm

If the surface of the mold is not glossy, the resulting glass form will not be glossy.

Mary Kay
Mary Kay Nitchie
Bullseye Glass Co.

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Re: devit issues - need help

Postby library » Thu Apr 18, 2019 12:14 pm

Mary Kay,

I do understand the main principles of casting - a mold produces a replica surface. The surface was not glossy in the original mold, but this wasn't the issue i had: I was having a white film appear on my glass. It turns out that i wasn't letting my molds dry enough. I kept them in a dry studio for about 2 weeks before - but it looks like they need about a month to fully dry in order to get the transparency I am looking for. I have attached pictures of a glass work that had a two month dry mold (clear green glass) and another that was only air dried for about 2 week (white scum on surface). Both pieces were made of same mold material, in same way, same firing schedule, cleaned in the exact same way.

At Bullseye how long to do dry your open faced molds for?

Best,

Richard Clements
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