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Coldworking with Loose Grit

For discussion and commentary regarding the Lesson and Project videos of the Bullseye Kiln-Glass Education Online program.

Re: Coldworking with Loose Grit

Postby charlie » Wed Jun 26, 2013 9:07 am

lbailey128@gmail.com wrote:I understand the loose grit method and have used it a bit with good success. However, I am a little puzzled by the sequence in the video where sections of the flat lip of a dropped bowl are scored, broken off and the bowl taken to the loose grit station. At first you can see that the ragged edges are there as it is beeing worked in the grit. Then those edges are suddenly gone in a following section, as if grinding vertically in the loose grit removed all the glass remaining from the scored/cut lip.

That's a long way down, does the video suggest grinding in loose grit to remove the remaining horizontal lip?

Could this same result be achieved more quickly by scoring/cutting as shown and then grinding down the remaining outside sections on regular rotary grinder? I assume that if this is possible you'd need to be careful not to stress the sides of the bowl against the grinder.


yes, you can score/break out, and/or use a regular diamond grinder to get rid of jagged edges. it's very hard to keep a planar surface on the rim though, since the contact point is so small. if you're concerned about doing that (and i have created non-flat surfaces doing this, causing long hours to fix), then using the lap/grit would be better, albeit slower.

i've also used the side of my wet saw blade for a grinder surface, especially on large and very thick slabs (>1"). be sure not to press too hard, especially on the thinner blades, to prevent a set in the blade if it gets bent.
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Re: Coldworking with Loose Grit

Postby marykaynitchie » Fri Aug 29, 2014 11:11 am

A cautionary tale:

We recently saw a pattern bar piece with little bits of gray and white contamination all throughout the surface in the Research and Education department. After looking at the piece under a magnifier, the gray was identified as silicon carbide and the white as glass dust. The maker had coldworked the entire surface of the piece, opening up the many tiny champagne bubbles just below the skin, which filled with grit and glass dust.

Please note that if you are using loose carbide grits to coldwork your piece, cleaning the glass before firing is important. In addition to wiping the surface with cleaner, we recommend using some sort of pressure washer or compressed air to clean the holes before firing.

Mary Kay
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Bullseye Glass Co.

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Re: Coldworking with Loose Grit

Postby Granatog » Mon Jun 15, 2015 8:40 pm

The video says dispose of used grit. The video shows washing it away, but where? Down a drain? Seems like a problem waiting to happen. What about rinsing equipment in the yard and letting the used up silicon carbide go into the lawn?
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Re: Coldworking with Loose Grit

Postby Chris_Petrauskas » Tue Jun 16, 2015 4:43 pm


Good catch!

Yes, the room we're working in in the video is a dedicated coldworking room with special traps in the drains to catch the fines.

You're right that you certainly would not want to send it down a standard residential drain.

As the grit is just a form of hard mineral, and that you're not introducing anything other than inert ground glass into it, adding it to soil should be fine.

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Bullseye Glass Co.
Portland, Oregon, USA
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