Schott S-8 Encasement Gobs

**Mike_Aurelius** · 01-13-2017, 05:55 AM

I discovered a stash that my dad had hidden. These are from the last melt Schott did of this glass probably back in the 80's or 90's.

15 pieces, 48 mm x 62 mm, ~15 ounces each
$45 each, plus postage.

PayPal only.

**istandalone24/7** · 01-13-2017, 06:32 AM

what is the coe of these? 106? 108?

**Mike_Aurelius** · 01-13-2017, 06:36 AM

108

**istandalone24/7** · 01-13-2017, 07:38 AM

i thought maybe that was the case, being it's s-8 (didn't know if the 8 was in reference to the coe or something).

are these compatible with moretti/effetre? i had some gobs from a while back, i don't recall which they were but they worked awesome once skinned down (flower compressions).

**dustyg** · 01-13-2017, 07:53 AM

Originally Posted by istandalone24/7

i thought maybe that was the case, being it's s-8 (didn't know if the 8 was in reference to the coe or something).

are these compatible with moretti/effetre? i had some gobs from a while back, i don't recall which they were but they worked awesome once skinned down (flower compressions).

S8 is supposed to be compatible with a fairly broad range of glass (because of the lead?). I believe that most of the people that use them use them with 90 or 96 COE, and 104 is easily compatible.

**Mike_Aurelius** · 01-13-2017, 08:22 AM

There's NO LEAD in the glass. It is Effetre/Moretti compatible. Probably not compatible with 90 COE glass, and 96 might be dicey.

**istandalone24/7** · 01-13-2017, 12:52 PM

if i end up selling a couple marbles today i'll take some, as i can't for the life of me find good 104 clear. of course these types of things always come up for sale when i'm broke lol.

**Mike_Aurelius** · 01-13-2017, 01:43 PM

LOL no worries. If you'd like, I can set aside a couple for ya.

**istandalone24/7** · 01-13-2017, 02:19 PM

if you'd do that, that'd be sweet! i'll definitely take 3 or 4 of them. i'm sure i'll waste one re-learning how to skin that shit. gets soupy toot suite!

**Lesbeatiques** · 03-04-2017, 01:06 AM

Are these still available?

**Mike_Aurelius** · 03-04-2017, 06:24 AM

I've got 14 of them, still available.

**brads** · 04-29-2017, 11:47 AM

I just stumbled across this thread. Mike, if your gobs are from the late '80's or early 90's they aren't from Schott's last melt of S-8, which was somewhere in the 2000s, but might be from their first one - the first that was released to the public, at least. Depending on who you do/don't believe, S-8 is a close lookalike to the glass that Paul Stankard contracted Schott to melt for him in the late 1970s. (Yeah, I know it should be "whom" you believe, but it just sounds weird.) I seem to recall that the first melt of S-8 they sold to the public was done around 1988 or '89. Prior to that, lampwork weight makers used Schott S-5, which has an expansion closer to the German color bar that furnace workers commonly use. I know that because I bought a pile of S-5 from Schott's last melt of S-5 in the mid/late '80s. After that they switched to melting S-8 exclusively (when melting glass for paperweight makers every few years). Some paperweight makers were not happy about that, and over the years I've sold off most of my hoard of S-5 to several of them.

Here's some info that may be of interest to people regarding S-8. The measured CTE (expansion) of S-8 is 109 from 20-300C, which would make Mike's stated CTE of 108 about right for a measured range of 0-300C. As he also said, there is no lead in S-8. There is some barium and there is some boron in it, along with the usual soft glass ingredients. But there really isn't anything magical about it. The composition is just very well thought out - and the glass skillfully melted in a well designed glass furnace by people who really know what they're doing, and aren't skimping on quality.

Information about the glass that some may have seen posted by a self-proclaimed "expert" elsewhere is largely bullshit. It doesn't contain a boatload of barium and it isn't a lead glass. (Both are claims that I've seen this particular charlatan make at various times.) I know this because I happen to know the composition of S-8. And no, I'm not going to share it with you. Feel free to whine about how unfair that is...

The primary reason S-8 "fits" 92-96 COE furnace glass is, well... it actually doesn't. But correctly done, the way a paperweight is constructed will keep it from cracking. Not surprisingly, most "104 COE" glass is a better fit for S-8.

Below is the data sheet for S-8. Note the date on it. If my memory is correct, and after 25+ years it is admittedly a little foggy, this was the second melt of S-8 that Schott made available to the public. The first one was a couple of years earlier. Prior to that, their melts for paperweight gobs (proper name: Art Encapsulation Glass) were S-5. I recently stumbled across my original invoice for the S-5 I purchased from their last melt of it. But, true to form, I've misplaced the invoice again. (I put it in the proverbial "safe place" so I wouldn't lose it.) If I manage to find it I can give an accurate date for the last S-5 melt and better determine when the first melt of S-8 happened.

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**BurntHands** · 04-29-2017, 02:05 PM

I find it strange that the refractive index of 108 coe is closer to quartz than boro is. I was asked the refractive index for boro by the faceters' guild as it affects the math for the cuts and angles to get the most bling, and I found conflicting info between 1.4-1.54 so we used 1.54, the index for quartz. I've heard stories of sci guys having a jar of refractive liquid around to ID boro - if they put boro in it it turned invisible but any other glass was slightly visible so they must be different. I later found 1.47 on a simax tech sheet, but this super soft glass has almost the same optical properties as pure quartz?

I heard Buzzini gave out all his encapsulation secrets on facebook when he retired. I bought a custom knight torch off him but I resold it to a member on here.
Does anyone still have access to this info or did anybody save it? I don't make paperweights or have a vacuum rig but I find that stuff interesting and I'd like to read it. It's not everyday a master just shares all his knowledge to the world - or maybe just a rumor?

I know it's a FS thread but its not really detracting and the threads not very active. If anyone's going to know about paperweights then there's a good chance they'd see this here, and its not worth its own thread...

**brads** · 04-29-2017, 02:50 PM

As far as refractive index goes, the COE of the glass is immaterial. The composition is what counts. You can have a high COE lead glass with a very high refractive index, or a low COE borosilicate glass with a low refractive index. And you can have the opposite, as well. The COE is completely irrelevant. Boron has a low refractive index and lead has a high one. End of story.

Likewise, your interpretation of the refractive index of quartz is seriously flawed. The refractive index you posted is for crystalline quartz, NOT pure fused silica. (Commonly, but somewhat erroneously referred to as "quartz" glass.) The two are completely different animals, and the refractive index of each is different as well. The refractive index of fused silica is roughly 1.45 at 589 nm (the sodium D line). Schott 33 COE Duran is about 1.47, as are most (all?) other common 33 COE boro glasses. For comparison, the refractive index of common soda lime glasses typically comes in around 1.5. Schott S-8 is probably on the high side of that due to the barium in it.

The liquid that scientific glassblowers used to identify boro is a mix of carbon tetrachloride and benzene, 59 parts to 41 parts by volume, respectively*. Due to the refractive index, 33 COE boro will disappear when immersed in it. I've been out of scientific glass for a long time, but I think the above mix has now been supplanted by something safer.

The info Chris posted isn't exactly "secret". A lot of paperweight makers already knew it. But yes, he was generous enough to share the engineering drawings and dimensions of his paperweight pickup apparatus. Whether or not he posted any other info, I don't know. The drawings are what I saw.

*Reference: "Scientific Glassblowing", Wheeler, pg. 53

**BurntHands** · 04-29-2017, 04:06 PM

Awesome, thanks! The quartz vs. fused silica thing seems so obvious in hindsight. I knew you'd have some input, but that's a really great post, glad I put my feeble thoughts out there! My limited search was a few minutes of googling (borosilicate refractive index), and the wikipedia rabbit hole took me to a bunch of different pages for oddball borosilicate crown glasses that I just skimmed over, but I got conflicting answers until I searched (simax refractive index) another time. I should have just asked you!

Good point about the leaded glass too, cut lead crystal throws some serious sparkle. I couldn't have cared less about RI until the gemcutters showed me flashy stones and the gemcad/raytrace software. Someone else might find them interesting, free trials.