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tinting billet on thick pieces

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tinting billet on thick pieces

Postby Kath » Mon Feb 01, 2010 1:06 pm

I'm hoping that someone can help! I have a commission to produce five thick discs that are 12" in diameter and 2.5" thick. The color needs to be consistent for the five pieces. I want the color to be just barely tinted off of clear. The pieces are to be fairly transparent. I have only kilns in my studio; not ovens for gathering and casting. Any hints on how I can tint the cullet or billet so that the color isn't streaky or spotty? Is it possible? This is the first kiln casting project we're doing and I'm a little nervous......Thanks, Kathleen
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Re: tinting billet on thick pieces

Postby Jim Jones » Mon Feb 01, 2010 4:47 pm

Hi Kathleen,

What color are you searching for? It is possible that we might have some curious/off-sample billets in stock that would work for you. Does the color need to be throughout the disc or could you use a thin sheet of transparent and back it with clear billets?

With some testing the frit tinting process might give you the correct color, but I don’t think that you would be able to eliminate the spottiness or streakiness even if you tried a pot melt.

Jim Jones
Bullseye Glass
Jim Jones
Bullseye Glass Co.
Portland, Oregon, USA
http://www.bullseyeglass.com
Jim Jones
 
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Re: tinting billet on thick pieces

Postby Kath » Tue Feb 02, 2010 1:15 pm

Hi Jim, The client is coming in on Friday. I'm not sure of the color, but I think he'll want a very slight tint. My initial impression was that he wanted one color throughout, but I'm thinking it may be more interesting (and maybe easier?) to do a couple of layers of color between some layers of clear. In that case it seems like I should just fuse the glass but we're used to making pieces 1" thick but not 2.5". I'm thinking that the bubbles would mess up the consistent color. For a girl who's been doing this for 25 years I feel pretty dumb....
If I wanted to cast and layer some tints and then some clear would I cool down in between layers? Would the "strata" stay pretty clear? The idea of reheating that thick slab 3 or 4 times seems risky. Thanks for your help. Kathleen (Kathleen Ash from Studio K; it's been a long time since I've spoken with you!)
Kath
 
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Re: tinting billet on thick pieces

Postby Jim Jones » Tue Feb 02, 2010 2:07 pm

Oh it’s you, Kathleen Ash. Great to hear from you.

We think you could get away with one firing and you would end up with nice champagne bubbles throughout the piece, but if you want to be certain that no bubbles are marring the surface we would recommend pre-fusing a core section, cool, flip and add layers to the bottom and top. This technique is discussed in TipSheet 3: Working Deep. http://www.bullseyeglass.com/pdf/technotes_tipsheets/TipSheet_03.pdf

Tell your client to embrace the bubbles in the glass, without bubbles he might as well be looking at plastic.

Jim Jones
Bullseye Glass
Jim Jones
Bullseye Glass Co.
Portland, Oregon, USA
http://www.bullseyeglass.com
Jim Jones
 
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Re: tinting billet on thick pieces

Postby johnreeves » Fri Feb 05, 2010 9:00 am

Hi there

I have used cobalt carbonate in either aquious or alcohol suspension thinly brushed on the surface, dribbling water or alcohol to dilute the layer of cobalt in interesting free form designs can produce pale blue abstract effects
(IF the suspension is dilute enough.) It will mature at casting temps. If sandwiched between clear, it will bubble excessively. The way to avoid that is to prefire the coated piece first.

With cobalt carbonate, less is definitely more. Too much, and you got the cobalt blues for sure!

John
johnreeves
 

Re: tinting billet on thick pieces

Postby morganica » Sat Feb 06, 2010 9:08 am

I will defer to the BE experts on this because there's probably a better way...but when I need transparency I have far more control over the glass color and bubbles by using a custom billet.

Make a refractory mold using a container that holds about 20% more than the volume of your model. (I used to use deli containers, then I had a set of well-drafted "mixing molds" made out of refractory) Choose a reservoir/crucible for your glass that you can prop as high up in the kiln and above the mold as possible. The idea is that the glass mixes and loses bubbles on the way down, so the more height, the better.

Set it up in the kiln and if you're using frit, block the reservoir openings with a couple of pieces of sheet glass to keep it from falling into the mold when it's cold (or you can prefuse the frit to a sheet of glass, just depends on how much work you want to do). Then start layering in your glass. The configuration of the gate (hole(s) from the reservoir), shape of the mold and the placement of glass dictate the color patterns in the billet.

You have to experiment to figure out how the glass will flow, but it usually pulls down from the center bottom, up through the center and across the top, and then from the sides. You can take advantage of this by stacking the reservoir horizontally--seems counter-intuitive, but you get a LOT more mixing action.

Then fire--I leave it at process temps sometimes for several hours to fine out the bubbles. I go for a fast anneal (I don't care if it breaks), take it out and see if I like the mix. If not, I break up the billet and refire it the same way. It'll also mix as it goes into the real mold, so keep that in mind.

This method opens up all sorts of possibilities if you start thinking about reservoirs, gates and the shape of your model. You can get some pretty stunning color blends and placements with it.
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