Comments on: Manufacturing jewelry with a Fresnel lens

By: rjl20: Street Fair Favorites

rjl20: Street Fair Favorites — Fri, 22 Dec 2006 16:09:19 +0000

[…] Josh (rjl20) wrote,@ 2005-05-24 22:37:00 Street Fair Favorites Some favorites from last weekend’s University District Street Fair:Verone Flood, photographer. She’s got some really nice compositions, and I like the triptych-like presentation style. There were a few designs at her stall that aren’t on her web site, and one of them I was thinking about buying. I guess I’ll have to email her and ask about it.Mud In Your Eye Pottery. They’ve got some beautiful glazes, and a very well designed mixing bowl. Also, a water crock that was too useful to pass up. I want to visit them next time I’m up in Bellingham.Sundrop Jewelry, glass jewelry made with a giant fresnel lens. Awesome. Cam posted about them, too.[ 5 Comments ] […]

By: Cam Sculpin

Cam Sculpin — Tue, 24 May 2005 05:01:53 +0000

I am always looking for a lecture on glass compatability. Thanks! Good to hear from you!

By: Hig

Hig — Mon, 23 May 2005 17:59:24 +0000

Ah, the internet…

I remember you buying the smokey bottle glass… It’s one of our favorite colors because it’s so unusual.

Too bad the weather didn’t allow for a demo this weekend.

I suppose you weren’t looking for a lecture on glass compatability, but…

Coefficient of expansion vs. annealing/tempering glass:

These are essentially two different issues. You do need to know the coefficient of expansion if you mix glass colors. This is why we do not mix bottle glass at all. We just use the bottle glass to make monochrome drops. If you mix glass with different coefficients of expansion, it doesn’t matter whether you anneal it or not, it’s likely to break. The multicolored glass is mostly Bullseye glass (we collect scrap from stained glass artists, and also buy some glass for colors we can’t find in scrap.) Bullseye produces all its glass with the same coefficient of expansion.

However you’re right, we do not anneal our glass. In many cases this would be a problem. However, because the Sundrops are small, and because they have a very simple shape (all convex in the area where it’s thick enough to have problems) it’s actually an advantage to temper (not anneal) the glass.

Basically what happens is that as the glass cools quickly, the surface of the glass becomes hard before the core. This means that the core overcontracts relative to the surface, leaving the core in tension, and the surface in compression. The compression means that it’s very hard for a crack to start on the surface of the drop… Similar to a tempered windshield.

Overall the drops are not tempered enough to ever “explode”. Some break during the process of handling them (particularly putting on the wire wrap.) It’s possible to more highly tempre drops to get “Prince Rupert’s drops” which do explode, see for example:

http://www.cmog.org/index.asp?pageId=735

By: Cam Sculpin

Cam Sculpin — Mon, 23 May 2005 00:47:22 +0000

Never have met him, as far as I know. Small world! Small town, anyway.

By: MaLora

MaLora — Sun, 22 May 2005 22:54:16 +0000

have you ever met Aaron Ford? he is friends wtih Jake & me and i know he’s met Josh. anyway, those sundrop earrings are made by his friends! i bought some last year as well.

the lens is awesome isn’t it?

By: Cam Sculpin

Cam Sculpin — Sun, 22 May 2005 02:30:31 +0000

Cissa: Got me. I know squat about glassworking. The glassworkers all still seem to have their eyes intact, though. Since they use scrap art glass for the multicolor drops, not bottle glass, they may have good information on those glasses’ coefficients of expansion. (And while they’re obviously proud of the multicolored glass work, from the looks of the stuff at the stand it isn’t most of what they do.)

I wouldn’t be too surprised if they had the occasional problem, though. I notice that they aren’t advertising for students.

Mallard: Saaaaaaaay. I remember that now. Ooh. I might be.

By: mallard

mallard — Sun, 22 May 2005 01:08:33 +0000

Saaaaay … I’ve got a Fresnel lens in my unused opaque projector. I think I offered it to you guys once before, but you were in the midst of a big decluttering stage. Might you be interested now?

By: cissa

cissa — Sun, 22 May 2005 01:05:37 +0000

Hmm. The jewelry looks really cool, but I’d be pretty concerned about the glass exploding at some point. When one combines glasses with unknown coefficients of expansion, that’s a risk- and even when things have similar coefficients of expansion, it’s a Good Idea to anneal the glasses after forming to prevent explosion from internal stresses. I don’t see how one can anneal with a big lens like that…

I don’t think earrings are all that dangerous, but it’s something to keep in mind for larger stuff.

By: Cam Sculpin

Cam Sculpin — Sat, 21 May 2005 23:19:06 +0000

Fire gardening! Yes, that’d take care of the grass just fine.

By: Ted

Ted — Sat, 21 May 2005 23:15:22 +0000

You NEED a giant Fresnel lens! Just think of all the… um… gardening you could do with it!