View Full Version : Calcedony Prep

Dan Vanantwerp
07-20-2017, 04:58 PM
Got the glass cooking for a cobalt calcedony.
I've been looking back at the various post notes for working this temperamental glass.
One thing Pete has pointed out is a tendency to lose the colloidal swirls of color due to the normal rotation of the pipe post-gather. His recommendation is a "slap gather". While this is a colorful adjective, I'm not quite sure what it means.
I'd like to have a good strategy for working the glass so I can best evaluate the cooking ingredients and make adjustments accordingly.

So, how does one perform a "slapped gather"? :)

-or does it take two?


Jordan Kube
07-20-2017, 06:42 PM
Don't worry too much about it. Anything you can do to manipulate the glass will make it fun. I like to drop some on the marver and then pick it up.

Dan Vanantwerp
07-20-2017, 07:12 PM
Ahhh...like the Dino Rosen video I watched.

I saw the torso pic you posted. Very nice!

Pete VanderLaan
07-21-2017, 08:02 AM
It's really helpful to not stir calcedonia glasses. If you do, they start to turn gray. So "slap gather" is just what it sounds like. Have an interior gather ready, as big as you want and then dip down on the side of that gather, lift up, rock it back and forth unless you like messes, and pull away from the pot. It will show the veining very clearly that way if it's a decent glass. I have seen people get directly above the pot and go straight down in and straight back up getting vertical veins. As Jordan suggests, you can lay out pieces of what ever shape you want on the marver and pick them up. Fred Warren was doing some beautiful work doing that.
I've long suspected that Dino as mercury in his calcedonia. I can't think of anything else that would make it so effective.

But don't stir it. It also likes to be thick.

Dan Vanantwerp
07-30-2017, 08:57 PM
Thanks for all the help. I feel like I owe it to CW to follow up with my results.

My first attempt was a cobalt mix that failed to produce opal swirls. I am using crystallica and wanted to see if the cullet/squiggles would work without fritting the glass.

I changed things up and made a clear calcedony mix (no cobalt) based on Pete's recipe for calcedony and fritted glass. Huge difference!

I'm loving this glass. My furnace is a custom wire melter in which is housed both my 80 lb crucible and a 17 lb "color" crucible I got from Sundance. I built separate openings for both crucibles. I just dip into the calcedony, pull out the gather and cut the tail with a pair of shears...no turning!

As the glass cools the swirls appear...more heat/cool cycles=more color!

I haven't quite got the red to express very well yet. Any advice to expand the color spectrum would be very welcome.

Thanks again to those who have shared their experiences with this color and especially Mr. VanderLaan.

Jordan Kube
07-31-2017, 04:06 PM
Add some copper and you'll really get to see those other colors expressed. Sometimes.

Pete VanderLaan
07-31-2017, 04:30 PM
Don't add much.... think mercury if you like life is the fast lane, sulphide form

Shawn Watt
07-31-2017, 05:36 PM
Ive got to ask .. how does the mercury act in the glass? I cant find any info on this.

Pete VanderLaan
07-31-2017, 06:46 PM
It 's an area to go into. Dino Rosin was getting reactions I have not seen and it's the only area where i haven't gone. My translator at the time was not willing to translate the observation for me at the time and I thought that was significant. That was at least ten years back and i never pursued it. I still have the compound. I was at a loss as to show how Dino got to the exceptional reaction he got otherwise on the guitars.

Eric Trulson
07-31-2017, 07:00 PM
Don't add much.... think mercury if you like life is the fast lane, sulphide form

Have any hunches as to whether you could use cinnabar in mineral form for this, or would you want to go with reagant-grade mercury sulphide?

I poked around a bit online, and the cheapest source I could find for 99% mercury sulphide was $80 for 50g at sigma aldritch. Easier on the wallet if you could get away with using crushed cinnabar instead. Or it might not be that big of a deal if the mercury is only getting added in very small quantities.

Mitcheal Veenstra
07-31-2017, 08:28 PM
wow! That's looking great!

so on our short list to try in the color pot this fall once we are back from Chuck's class at corning.

Dan Vanantwerp
07-31-2017, 08:46 PM
I was working with the color again today and it started to get a little muddy. Remembered what Pete posted once about hitting it with acetylene to "wake it up" and it seemed to help.

I'll try the copper addition and will get back to the cobalt as well.

I found that it could also be left on the surface and even did a stannous treatment that looked really nice.

Pete VanderLaan
08-01-2017, 06:32 AM
I would certainly try the cinnibar. I'm not really familiar with it. Glass never needs more than technical grade and the only thing you have to watch out for in compounds is to note what's there in what quantity. I think the mercury would be in very minor amounts if it indeed did work.Everything's minor. I think the silver nitrate content in a proper reducing glass body is 9 grams in 21 pounds.

The calcedonia does work best in the presence of a small amount of red iron which is a nucleator. The chemistry of he goop is long strands of molecules that absorb and reflect with variation. The effect is best when the molecules are large and they do gradually get smaller so the effect decreases. It works best in a high potassium glass and none of the cullets have potassium to any degree. They want cheap glass and it's why I make my own. As noted, stirring it makes it worse as all the color effect mixes and turns gray. The heavy reduction from acetylene does help but there's nothing like a nice fresh pot. Eventually it will turn transparent amber. Doing the cobalt becomes a fine line between too much and too little. Copper in very minor amounts causes a red strike in the lehr.

Dan Vanantwerp
08-01-2017, 09:42 AM
Hi Pete, To your (extensive) knowledge, do any of the commercially available batch mixes have a good potassium content for the purpose of calcedony?

I am slowly moving toward mixing up my own glass but in reality my space would not lend itself to a high volume chemistry area.

Pete VanderLaan
08-01-2017, 10:45 AM
I wrote the best clear formula I've ever written for Spruce Pine last year. It's what I use but Spruce Pine has indicated that it does not want to produce the stuff because they have trouble storing Potassium compounds, SO Jim Myers at East Bay has indicated that he will produce it but it won't be pelletized. It's a custom batch at this point and not a stock item.
When John Croucher and Mark Peiser and I were bouncing these ideas off of each other, I submitted this one to John at near the end of two months work, he looked at it and said "I cannot find a single thing to object to in this glass". I wrote a second formula to marry to it which is unoxidized, which is important.

For me that's the highest praise I can get. I think the world of John and Mark. We had the best dinner at Tony R's with Eveline from Shanghai at Corning last June and simply closed the restaurant.

Dan Vanantwerp
08-02-2017, 02:13 PM
I've contacted Jim and left a voicemail. When it's available, I'm hoping to get some of your potassium batch to optimize the calcedony effect. I'll test the compatibility with Crystallica as an encasement glass and see what happens.

Pete VanderLaan
08-02-2017, 02:19 PM
He'll need the formula, but Jim and I always like talking to each other. Old War Horses.

Scott Novota
08-03-2017, 11:42 AM

How would the formulas from the class marry to your new batch?

Pete VanderLaan
08-03-2017, 12:53 PM
There are two different batches. The one I primarily tout as great is a Clear formula with a barium presence, little calcium and no borax but a lot of nitrate. I would not be inclined to use it as a calcedonia base but it could work, it will just take extra black tin and probably more silver to fight off the nitrate,

BUT... It is also designed to marry to the unoxidized formula which I provided the class years ago. If you were matching it to Cristalica ( which is how it's spelled) the Cristalica would be about a half point higher than mine which is tolerable. Mine just sits on SP87 as the target expansion.

It might be the case that either Spruce Pine or East Bay could mix that since it contains no nitrates at all eliminating the hydrophilic tendencies of potassium that Spruce Pine has problems with. Neither has the formula but I can provide it to them.

Dan Vanantwerp
08-03-2017, 02:01 PM
Jim called and sounded interested in batching your formula. He wanted me to pass on my furnace specs. It's a wire melter and he is concerned about melting batch in it..specifically if it required higher temps. Funny, I was just reading the Antiques and Classics thread on this issue the other day. I do recall that you like to melt calcedony at a lower temp (2180, I believe) which my furnace can easily handle. Would this also be the case with the potassium glass?

Sounds very doable to me. I'll only be doing small batches in a 17lb crucible. The furnace is made to keep the majority of the crucible contents away from the elements. I can live with some loss of element life if the colors blow me away.

Pete VanderLaan
08-03-2017, 02:25 PM
I will need to know what mesh sand Jim uses and it really needs to be a 200 mesh. Since he doesn't pelletize, it can work. You just have to charge in tiny amounts. There's nothing in it that would attack your elements. I need to talk to him anyways and always look forward to it. The number of people you've known fifty years at this can be counted on one hand usually.

What I don't know is how much a minimum for him to mix is. If you were doing the unoxidized, it would take a long time to use a ton.

Dan Vanantwerp
08-03-2017, 02:55 PM
I made it clear to Jim that I would be experimenting to start with and that I am not a big production studio (I usually only buy 500 lbs of Cristalica at a time). He sounded OK with that.

Sorry for my spelling errors...I probably don't have calcedony right either (Chalcedony?).

I'll let you guys take it from here and look forward to trying it out.

Scott Novota
08-03-2017, 04:42 PM

Please let me know when you have this locked in I would like to give it a run myself. I would not mind pulling smaller(500lbs) order to start off with to give a go.

Pete VanderLaan
08-03-2017, 06:01 PM
It's been locked in for a year now.

Jim and I talk like we're both going to the beach and who cares.? We'll get there.

Scott Novota
08-07-2017, 03:20 PM
Well I cooked some up over the weekend in the mini furnace. Figured I would add my tumbler to the mix. It really blows my mind that it comes out of the crucible clear.

Using it on the inside of Conch shells but they are all still in the hot box.

Pete VanderLaan
08-07-2017, 04:56 PM
well done!

Dan Vanantwerp
08-07-2017, 05:30 PM
Awesome color spectrum Scott. The clear to opalized transition is a bit like magic. Would be great for live demos. I had a show this weekend and all the customers were drawn to these pieces. Inside of a conch shell will be a great application.

A bunch of boro artists came by and suggested that it looked just like "amber purple" in the COE 33 world.

The matte finish suggested by Sky on my other thread was pretty damn amazing. I didn't think it could look better but I have to admit that I like it even better.

Please post pics! I'll upload an image of the matte finish later.

Pete VanderLaan
08-07-2017, 07:13 PM
matt, blasted in contrast is remarkable/ oil it.

Jordan Kube
08-07-2017, 07:50 PM
That's the stuff

Mitcheal Veenstra
08-14-2017, 01:43 PM
that's really nice

Greg Vriethoff
09-16-2017, 10:38 PM
I'm nowhere near being able to play around with any of this stuff right now, but it gets me really excited to see what people are doing. I can't wait to get things up and running around here.

Thank you to everyone for sharing here.

Pete VanderLaan
09-17-2017, 04:37 PM
Actually, this not a hard glass. It does depend on the basic clear formulation. It would probably be equally relevant if I had a class on clear bases for colors but it is not sexy. In all my correspondence with John we talk base glasses more than anything. I don;t think anyone pays a whit of attention to those basics. I think I have five bases and John, last time I checked, has nine.

Once through the base, then apply the rules for expansion and viscosity. Make it fit.

Dan Vanantwerp
12-21-2017, 03:04 PM
Been working with the cullet formula for a while now. I'm trying to achieve more of the blue, lavender, red colors and less yellow-brown. I've recently tried 5g cinnabar in an 8lb mix of the normal chalcedony formula (no cobalt or copper) from Pete with no obvious benefits. I realize cullet could be my limiting factor and that whatever reduction state is needed for the "lovely" colors may be limited in an oxidized base glass. My ventures into batch are awaiting the availability of the commercial batch guys.

I did run across an interesting excerpt from Charles Bray in his "Dictionary of Glass" while looking up the possible effects of mercury in glass. I don't have the book (yet)....this came up in the eBook preview from Google.

from page 102...Into this was added a mixture of zaffre (a type of cobalt silica), iron oxide, copper oxide and mercury sulphide dissolved in nitric acid. The resulting glass was worked at the furnace in the normal way, but in common with some coloured glasses such as copper, gold and selenium rubies, it was necessary to get the colour to strike. When ware for such glasses are made the metallic crystals formed during the initial cooling are very small but reheating at the glory hole can be...

I can't wait to get the book and read the context and conclusion of this paragraph. Based on this, perhaps the cinnabar requires pretreatment with nitric acid...pretty nasty. The info I have read suggests this requires boiling temps on top of the already dangerous chemicals involved. OR...they are just dissolving everything in acid and the only benefit is to create silver nitrate. Any thoughts?

Pete VanderLaan
12-23-2017, 12:11 PM
I never found Bray to be really informative at all. I do have the mercury sulfide and have yet to try it. I do use copper in it as well as occasional cobalt salts.

The effects Dino Rosin has gotten are by far the most remarkable I've seen. I did the work for Simpson's Corona stuff.

Dan Vanantwerp
12-28-2017, 12:55 PM
I'll have to give the cobalt salts a try...only ever used oxide form. I'd like to maximize the amount of black tin for use in cullet. Also, in looking back at the original recipe you mentioned using window glass with a relatively high iron content. I'm going to try and find the optimal iron content for cristalica. It has seemed to help to bump up both the black tin and red iron in my preliminary deviations from the original. Some have mentioned sugar as an alternative reducing agent. Lots to try...just wish I had a couple more color pots.

Pete VanderLaan
12-28-2017, 01:50 PM
If you push the iron too hard, it won't opalize. Sugar doesn't really work unless it's very short term with gas. Black tin is really the reducing agent of choice. The Mercury really is an unknown for me.

Dan Vanantwerp
12-28-2017, 02:53 PM
I've eliminated the zinc with no change. I was trying to remove some of the off-white, yellow to beige opals but they still develop. The tin seems to push toward the purples, greens and blues. Wish it wasn't so pricey. I'll also try less silver. The reds in these photo are what I'd like to achieve. I sure didn't see anything start to pop out with mercury, but I'm far from exhausting the possibilities with it.

Pete VanderLaan
12-28-2017, 03:54 PM
you have nothing to complain about.

Dan Vanantwerp
12-28-2017, 05:10 PM
Sorry...the pics are not my work. That's Dino.

Here is a platter from Josh Simpson with the red color spectrum highlighted...this is the color I've yet to see in my own work.

No complaining here...I'm very happy with my results. Just curious about the red not coming through...yet :)

Pete VanderLaan
12-29-2017, 07:05 AM
It comes from red copper. Run your annealer hot. It will strike there. We periodically threw small wax balls onto the pot surface before the slap gather, sometimes we used an oxy acety;ene torch briefly on the surface. Don't gather, slap.

Dan Vanantwerp
12-29-2017, 12:05 PM
Thanks Pete. I'll give it a shot. My color pots gather vertically which works nicely for the colloid formation. The hotter anneal is going to be interesting...I recall Jordan Kube also saying the red copper strikes in the annealer. I'll bump it up 50 degrees or so.

Pete VanderLaan
12-29-2017, 01:14 PM
do keep in mind with Dino's, he's using more than one pot of glass. As to Josh's, that's not really a very good example. we did a lot better than that.

Jordan Kube
12-29-2017, 03:19 PM
Don't forget, process plays an important role in color formation. When I slap a large gather of chalcedony on the marver and pick it up on the side of a solid piece of clear to sculpt, it's nothing like blowing. I would go so far as to say it's an apples to oranges comparison. They've found that color formation in these types of silver glasses depends not only on the size of particle but also the shape. Good luck getting a handle on that! I'd love the hear about your good results though. I'm on the same path right now but with nothing significant to report.

I've found I can get Dino like results with the process I described. Doesn't look exactly like his but I've never been able to touch these colors blowing. I would stay away from mercury. There's a reason nobody uses it.

Pete VanderLaan
12-29-2017, 03:46 PM
seriously, mercury is no worse than lead or Cadmium. Gloves and ventilation, wash rinse repeat...

Hard to get though

Dan Vanantwerp
12-30-2017, 02:28 PM
I've ordered some more of it on ebay. It's the only place I've found...straight from Hong Kong. Reasonably priced.

The results from Josh Simpson and Pete are mostly blown. Dino does some bowls also with nice color results. That pink-lavender-red transition is my goal, currently. I start my day with a little solid work just to see the look of the glass. I agree that it likes to be thick. However, I did make some ornaments for co-workers and they looked pretty nice aside from the tiny pin needles which only I seemed to notice.

I'll keep plugging along with it and will be happy to share results.

Pete VanderLaan
12-30-2017, 05:19 PM
saying "it likes to be thick is another way of saying, "It likes to be cooled slowly". Think on that.
Then Think on the notion that I don't think anyone's holding out on you. They;re saying there's a lot of stuff that hasn't been done. Some will be crap, some may not be.

This has been going on for four thousand years. Think on that. You have giants around you. You need to add to the knowledge.

Dave Bross
12-31-2017, 04:22 PM
My understanding of Mercury is that it is WAY more toxic than most things, particularly vaporized.

Be damn sure your ventilation is up to it if you choose to use it.

Years ago people were experimenting with Mercury as a weight shifting mechanism in stock car racing. It was banned on the premise that if a few drops of Mercury found their way onto the hot manifold in a wreck the vapor could be fatal to anyone nearby.

Here's more on the subject:


Google has more.

Rich Samuel
12-31-2017, 04:52 PM
Years ago people were experimenting with Mercury as a weight shifting mechanism in stock car racing.

Better to stick with moonshine.

Of course, when I'm looking for safety advice stock car racers are the first people I consult. :D

Brian Graham
01-01-2018, 08:13 PM
The copper ruby matrix....copper, iron, black tin, and silver nitrate in cullet.


Pete VanderLaan
01-02-2018, 05:58 AM
seedy though....

Pete VanderLaan
01-02-2018, 04:17 PM
Don't forget, process plays an important role in color formation.
I've found I can get Dino like results with the process I described. Doesn't look exactly like his but I've never been able to touch these colors blowing. I would stay away from mercury. There's a reason nobody uses it.
Bingo by the way! This glass wants different temps to get a strike. Then it wants a range in the lehr. Rod always looks better than the result using rod. This is glass that wants wretched excess and I think that's true in almost any really good glass I can think of. If you want gold ruby, you need pounds, not a chunk of rod. Making spectacular artwork involves lack of consideration of the materials you use. In reality. Gold Ruby costs about a buck a pound if you make it. Silvers are substantially less. The bottom line is to believe and make the jump. More and more of you are indeed doing it and you will benefit.

Mercury in my mind, at 68 is worth the pursuit.

Dan Vanantwerp
01-02-2018, 04:37 PM
Thanks for the color sample Brian. I like that spectrum! I'm getting some pretty similar results with a fresh pot of the same ingredients you listed. Your backlit example (right side) makes me wonder if I'm chasing a lighting trick with the reds.

However, the pic of the Josh Simpson platter I posted looks like a fairly candid shot taken on someones deck. Some of his work is photographed in a light controlled setting and makes me wonder if things are being a bit enhanced. The area I've highlighted looks like a brilliant orange-pink-red...just would really like to see that come out straight of my annealer someday.

Pete, I'm not suggesting anyone is holding out, but I'm not always the sharpest tool in the shed either. When I read that this color likes to be thick I thought about color density...not anneal time. To me, thick=less blown. I've turned up my annealer as a single variable but can also adjust for a longer cool down. Thanks for talking slowly when it's obvious I'm not getting it. :)

Perhaps I can add something to the knowledge with my experiments with mercury in glass. It does scare me though...Dave and Rich's point is well taken. I've attached one of the very few things I've found relating to mercury as a glass pigment...seems alone to give a yellowish hue.

Pete VanderLaan
01-02-2018, 05:34 PM
If it's a sulfide, more likely that's the sulfur.

Dan Vanantwerp
01-04-2018, 06:29 PM
The above photo of rare earth glasses was lifted from a lecture by Dr. James Shelby, professor emeritus at Alfred University. Here is his response to an email request for clarification on the composition of the Hg labeled glass.
The full lecture can be found here:

"I am very sorry, but there is no mercury in that glass. My handwritten notation is very poor. The ďgĒ is really an ďoĒ. The glass contains holmium, not mercury. Although I have personally made a few thousand different glass compositions, Iíve never tried to put mercury in a glass (there are several elements I refuse to work with due to toxicity, including mercury, cadmium, tellurium, and selenium ó probably some others I donít remember right now).

I have read some place about getting some mercury into oxide glasses, but donít have any idea where. I think it was from work very long ago.

Sorry I canít help you on this. I never noticed how bad my lettering was on that slide. Hope no one else was misled.

James Shelby"

Dr. Shelby went on to offer some info about his work on colloidal formation in glass:

"On a separate subject, I did a lot of work on colloids my last few years before retirement. Had a lot of fun working with silver and copper, both with reduction using the tin in the surface of float glass and with reduction using hydrogen. A lot of the work involved diffusing the coloring ion into the glass by exchange with alkali ions in the glass. Since Iím not an artist, I never worked with the traditional method of striking to form the colloids.

We also worked with lots of other colloid formation. Arsenic and antimony formed brown glasses in low concentrations (less than 1 wt%). We also made colloids of nickel, cobalt (both magnetic), lead, bismuth, indium. All of those ions result in black glasses.

James Shelby"

Finally, I suggested that he might visit the Craft Web forum to learn about the artists' pursuit of color and glass chemistry. What a surprise response!

"...I would be interested in viewing your forum. While my own experience is in glass science, my daughter is an avid glassblower. We have had many interesting discussions regarding color form our different perspectives. Perhaps I can contribute to your forum from my perspective as well.

James Shelby"

Does anyone know his daughter? Is she possibly a member of the forum?

This really made me smile :)

Pete VanderLaan
01-05-2018, 06:40 AM
I find it odd that he would avoid selenium. It's hard to do a lot of color without it. The multi valent atoms are usually your friends.
I would say once again that the morbidity stats on people who melt glass just really show very little effect. The things that are killing off glassworkers are alcohol, tobacco, obesity and Cholesterol. A fair number have had heart attacks or blood clots. I know of one cancer of the kidneys but metal poisoning? I know of two in fifty plus years and they didn't die of it. They both recovered. In both of those cases, the circumstances were egregious.

Eben Horton
01-05-2018, 06:53 AM
I find it odd that he would avoid selenium. It's hard to do a lot of color without it. The multi valent atoms are usually your friends.
I would say once again that the morbidity stats on people who melt glass just really show very little effect. The things that are killing off glassworkers are alcohol, tobacco, obesity and Cholesterol. A fair number have had heart attacks or blood clots. I know of one cancer of the kidneys but metal poisoning? I know of two in fifty plus years and they didn't die of it. They both recovered. In both of those cases, the circumstances were egregious.

Rob L. Had cadmium poisoning in penland years ago due to poor ventilation.

Pete VanderLaan
01-05-2018, 07:44 AM
Rob is one of the two I referred to. He was melting an opaque yellow for the Banana pieces and had a fan blowing warm air from under the hood to heat the studio. He did have extensive Chelation Therapy for it. The other was Hugh Jenkins when he was a grad assistant at RIT way back in the seventies as well. His professor had him melting a lead arsenate white every night in an unvented studio. That got the program shut down.

Those are to only two documented cases of that type of poisoning I know of. Paul Marioni did get extremely sick from eating a sandwich he got from a dumpster back in the mid seventies as well. I believe that was antimony poisoning and there's something to be said for not eating out of the school garbage can.
My real point there is that ventilation, gloves and a respirator are key to making your own glass. Casual use of a powder booth is another potential source but the facts don't aim at lung cancer from fiber nor kidney or liver failure from fumes. It's lifestyle that kills you.
Fritz has been melting batch glasses all his life. So has Mark Peiser and many of the renaissance glass instructors from the '60-90 period did as well. John Triggs died of a heart attack, Peet Robison, a blood clot. Henry Summa did die of Kidney cancer but he was never what I would call healthy during his life having had Hepatitis early on. All these guys melted raw glasses a lot. Dreisbach and Peiser are about 80 years old now. They're fine. Penland people have done raw glass forever. Levin was the only one to ever get ill.

Eben Horton
01-05-2018, 09:22 AM
I think of elio quisari (sp?). He swore by his Teflon parchoffis. Died of lung cancer. I have always wonder it it was related.

Pete VanderLaan
01-05-2018, 10:05 AM
John Chiles ex wife used to be on a tear about having blood testing for people in art studios. It was a big push she made while on the Board of Gas. Then I found out she was a smoker. It's the first question I always ask when people die of lung cancer.

Was he a smoker?

I have always heard teflon was toxic but I don't really have anything to back that up with. I never used the tool.

Jordan Kube
01-05-2018, 03:55 PM
The insidious thing about Teflon is it accumulates in your body and doesn't leave. Once it's there it's there. It's been deemed "safe" for cook ware but only if you don't get it above a certain temperature. We are definitely using it at higher temperatures where it can smoke and enter the body. Boy are they smooth jacks though.

Pete VanderLaan
01-05-2018, 05:11 PM
I've been at it since I was 19. I'm 68 . We're all going to die. I think if anyone tried anything risky, I did. I was never stupid about it, never contemptuous. Learning is a process.

Eben Horton
01-05-2018, 05:23 PM
The insidious thing about Teflon is it accumulates in your body and doesn't leave. Once it's there it's there. It's been deemed "safe" for cook ware but only if you don't get it above a certain temperature. We are definitely using it at higher temperatures where it can smoke and enter the body. Boy are they smooth jacks though.

I had bought a couple sticks and made a pair back in the 90's. I distinctly remember opening up a piece that was clear and got a huge waft of a nasty chemical smell. Off they went and into the trash can.

Josh Bernbaum
01-06-2018, 08:26 AM
They had the teflon sticks for parcioffis at the studio in Japan where I recently taught a workshop. They recommended holding my breath while I used them, so I asked them to put wood sticks in the handle I was using instead. I've been around enough nasty shit so far, don't need to be exposed to any more..

Dan Vanantwerp
01-06-2018, 02:07 PM
Here's an article about teflon toxicity...read on if you want to like Dupont even less.


Pete VanderLaan
01-06-2018, 03:21 PM
teflon, including the stuff in our kitchen never seemed like a good plan to me. I had a stick and only used it once. Cadmium? Now Cadmium I like....makes this yellow.

Steven O'Day
01-06-2018, 05:33 PM
Fritz had zinc shakes. Don't think he ever figured out where it came from.

Ventilation is good but think about where it goes when it leaves the vent as well.

Steven O'Day
01-06-2018, 05:39 PM
I vaguely remember Elio mentioning that he smoked but gave it up.

Pete VanderLaan
01-07-2018, 05:59 AM
Fritz had zinc shakes. Don't think he ever figured out where it came from.

Ventilation is good but think about where it goes when it leaves the vent as well.

Dan Vanantwerp
03-10-2018, 09:52 AM
My chalcedony has become very dark, swirless and seemingly colorless...sometimes it looks amber, sometimes blue and when I peer at it from certain angles even green. This color still forms upon cooling but the colloidal strands look like fine threads with little color variation. Seems like what Pete has described as small molecules that occur with too much silver or black tin. That, and the colors I see, suggest to me that I've got too much metal; the iron, silver and copper may be hanging out in the bottom of my small pots and corrupting my attempts at a calculated mixture.

If this is true it must happen to those who mix colors alot. I worried about "drilling" these pots but they seem to be holding up well. At the end of a shift, I dump their contents and make frit. It use to work well to remelt this frit both that has gone off as well.

Would a periodic clear wash make sense...or even a 50% metals batch to try and achieve the proper final mixture? Wondering if this is a common problem.


Pete VanderLaan
03-10-2018, 12:23 PM
There is always a temptation that "more is better" in opals. It's not the case. Less is better is really the approach. Just right is better still. Calcedonias in my experience want very little silver, and if the tin gets too high, it will reduce everything in sight and turn dark. It has a lifetime in the pot as well. Atmosphere also matters- nice and neutral.
I don't believe I've ever drilled a pot with metals, at least not since about 1974.