Thanks for all the comments on clay...now I have food for research. Clays to investigate. I have been using Highwaters desert buff and it is acceptable, but I want something with better vitrification at cone 5/6. 

Drying slow is always good. Cotton sheets or fabric of any type sometimes works better than plastic.

I use Highwaters desert buff and it is made for cone 5/6.  I have had no problems with it at all.  By the way, I also use vinegar and no slip to attach my handles.  I have never, knock on wood, had one crack off:>)

Highwater has an earthenware called Bella's Blend that claims cone 6. I just started cone 6 firing using stoneware and had to make an earthenware peice for my aunt and decided to try the leftover Bella's at cone 6. The glazes I'm using worked as well on it as on my stoneware and it vitrified very well. If you fire it any higher than cone 6 you can have some trouble, obviously.

I highly recommend the the Steven Hill DVD to anyone who wants to learn about layering glazes, use his updated cone 6 glazes and/or firing schedules, get a feel for the man himself before doing his workshops, or as a refresher if it's been a while since you attended one of his workshops.

This  was Posted by eleanor akowitz on December 3, 2010 at 1:59pm in Continuing Education. It got no responses there, so I'm moving it here where more people may see it, and follow the link to see the photos from the Steven Hill workshop she attended.

Hello SHO Project,

Can anyone tell me (or show images) of the difference between the cool and warm versions of Strontium Crystal Magic? I downloaded a free file from Ceramic Arts Daily (free subscription required) and it listed both recipes. Link. Just curious if anyone already has some side by side comparisons. Eventually I hope to post some of my own.

Also, have there been any tests of the "food safeness" of SCM? I've seen it used on the insides of bowls but other people use a liner glaze and only have the SCM on the outside of pots. I haven't seen anyone share actual test results.

Sorry if this has already been discussed. I'm still learning to navigate the site. There is a lot of good info!

Brandon, basically the Warm SCM is a more earthy yellow/brownish color after firing. You use it with warm earthtone color schemes, ie. with yellows, browns, greens, iron saturate reds, etc.  The Cool SCM is more white in color and goes better with a cooler, ice-like pallet of blue, white, grey, black type of glaze colors. If you get Steven Hill's DVD he shows examples using SCM Warm & Cool versions. I mostly work with the SCM Warm but have done a few pots with the SCM Cool.

The two are the same base, but cool is white, warm has iron added that gives it some yellow. Neither is particularly attractive alone, and are always used as base glazes, under several or many layers of other glazes with multiple heavy metal colorants.

How would you reliably leach test all the possible glaze interactions and the stability of those blends? It might give some comfort to have samples of your favorite combinations leach tested, but you still couldn't guarantee future results.    

Brandon,  The Steven Hill portion of the download offers good examples of the SCM Warm versus Cool SCM on pages 5 (warm)and 6 (cool).  He uses a warm palette SCM Warm base, and a cool palette, Cool SCM base).  About 80% of a pot gets the SCM base, then 4-5 glazes are layered over.  The top and bottom, or edges will typically get a contrasting glaze.  Several good examples in that article.

Hey guys, thanks for the comments. I thought the warm and cool versions were pretty similar, I just hoped to see if there was a discernible difference if they were both put under the same glaze. I suppose it could be different for every glaze combination.

George, I was expecting an answer like you provided. Probably too many variables for anything conclusive. It would be interesting to see how stable the glazes over SCM are compared to the glazes by themselves.  I've looked at Steven Hill's site and he has a lot of great functional work but I haven't seen any mention of leach testing. Maybe I'll try to contact him and see what he has to say.

Thanks again.

I know of four different versions of Hannah's Fake Ash, none of which include silica - so you have a fifth recipe!

I obtained this version of Hannah's Fake Ash from the potter Yoko Sekino-Bové.

100.0% Ellen Shankin’s Fake Ash ^5 -10
60.0% Redart Clay
30.0% Whiting
10.0% Barium Carbonate

I too have found the SCM warm and cool very similar.  Cool on the left and Warm on the right.

SCM-Warm is slightly more fluid than SCM-Cool, due to the higher level of Custer Feldspar, and of course yellow-orange colored from the Yellow Iron Oxide not in the cool version of Strontium Crystal Magic.

The Hanna's Fake Ash I've seen around for years and which I use frequently for Cone 6 oxidation glazing is:

Hanna's Fake Ash:

30 - Whiting

10 - Strontium Carbonate

60 - Redart Clay

Add: 3.5% Red Iron Oxide

        3% Yellow Iron Oxide

For Yellow: add 4% Ochre

For Blue Add 1.5% Cobalt Carbonate or around .75% Cobalt Oxide

No Silica in the Hanna's Fake Ash recipe that's been around a long time.

anyone know what S Hill's most recent firing schedule is ?  I know he changes this, holding at approx 1600 degrees.  Trying to program this schedule in my kiln.  

Thank you ,   cp  by the pond , now with two bee hives !

Diane, I look forward to seeing your results.  I switched to Laguna's Red Rock this year.  I love the look of it raw when slightly over fired.  I am having to look for new glazes too.  I love the look of Steven Hills glazes but spraying isn't an option for at this time. I'm wondering if the same effects could be duplicated by pouring with thin glazes.

I just joined the group and I'm reading the posts so excuse me if this is answered elsewhere. I the new updated Steven Hill DVD available here in this site? I am not seeing it on the home page of his site. The DVD on the ceramic arts daily site looks like it is not an updated version. Does someone have the link to the updated version? Thanks

I am assumeing that Glazemixer is out of business. Does anyone know?

The GlazeMixer website is temporarily down for maintenance.

It may take us a few days to finish everything.

If you have any questions, please contact us at customerservice@glazemixer.com

Thank you for your patience.

https://www.glazemixer.com/temporarilydown.htm?aspxerrorpath=/defau...

We have reports of glazemixer.com being temporarily down starting in January. I checked on them a couple of times with the same result. This type of notice without updates usually means permanently down. 

The Critter Siphon Gun..... wondering which compressor would operate well with this gun? Anyone using this ystem?

Joan - The Critter needs 3 cfm (cubic feet per minute) at 90 psi, according the page on Amazon.com

Critter Siphon Gun on Amazon.com

Just below is the section "Customers Who Bought This Item Also Bought" which shows some $100 compressors with higher PSIs, so the pump or the critter needs a pressure valve to reduce the pressure to the Critter. And these pumps have lower cfms, (a lower flow rate) which is why a compressor has a storage tank.

Based on my limited experience with compressors, another important attribute to consider is the noise level they produce. Sadly, less noise tends to be associated with a higher price.

Comment by Joan Scott 4 hours ago
The Critter Siphon Gun..... wondering which compressor would operate well with this gun? Anyone using this system?

Cone 6 firings can be done with a non digital kiln. The firing is usually done in three stages, LOW... set for about two hours to drive water out of  the clay, MEDIUM for about two hours to get the temperature above the quartz transition, and then full on HI to bring the kiln up to the point that the kiln sitter turns it off.

People use all kinds of variations of this for years.  You will have to experiment around. There are a lot of factors that will change the ramp timing.

The down side is that it is hard to track variations in the ramp as you can with a digital controller. Also you can't easily  do a hold at a given temperature, or control a negative temperature ramp to a lower temperature.

There are plenty of people out there who have been making great ceramics this way for years.

Thank you for your comments, John and Robert.  I have a pyrometer, so I will experiment and let you know how it goes!

Down firing a manual kiln is discussed on the network at http://cone6pots.ning.com/forum/topics/how-to-downfire-a-kiln-sitter

Steven has had more impact on my aesthetic and process than any other single ceramic artist. I was very lucky to attend a 4-day hands-on workshop with him in 2009 when he was just making the transition from gas reduction firing to electric firing, while experimenting with glazing techniques to retain the look and feel of his finest reduction fired ware. Ceramic Art Daily has a new article from Steven for your perusal. 

I have a question about SH's pots. I have tried using SCM, I get some really nice results, but the glaze surface always feels so gritty and sandy. It isn't really sandy or gritty but the feeling is rather odd. Does anything else get anything like this or I am doing something wrong?

My impression has been SCM requires more than a Cone 6 to achieve the results I see others showing. The same too with Jen's Juicy Fruit. For me at Cone 6 both have too much unmelted materials - particularly the strontium in SCM.

So you think I should try getting closer to cone 7? I can do a hold at cone 6 and hold for like 30mins or something and see what happens.

Catherine Rehbein fires a lot of clearly glossy melted strontium crystal magic pieces, so I'd be very curious what firing she uses to achieve this. http://cone6pots.ning.com/profile/CatherineRehbein

Strontium oxide produces brilliant colors like lead with low thermal expansion and can be a flux above Cone 2.  But Strontium Carbonate doesn't decompose until an astounding 2,721 F, a good 350 F hotter than Cone 12.

If you're interested in an experiment, before adding the strontium carbonate to the glaze, I'd first react it with an acid like vinegar or hydrochloric acid to release the carbon dioxide.

Strontium acetate and strontium chloride both decompose below Cone 010, but at the expense of being far more soluble than strontium carbonate. I'm curious if this would make any change in the firing behavior of SCM.  It seems unlikely but potential surprises lie in wait out there.

So soaking strontium carbonate doesn't sound that hard. Do you think it would fully absorb into the vinegar? Or do you think if I evaporated the vinegar it will return to a type of powder?

I guess I will have to test and see. Im thinking I will mix a 2 test batchs of SCM, and a control batch. I will put the stront carb into the vinegar and let it soak overnight. I will then just directly pour one into the glaze mixture and then adjust flocculation with darvans. Then I will take another vinegar batch and try to dry it out and see what happens. If I can dry it out I will run another test using that SCM batch, and I will run a control batch just to compare. I will run the test using currie grid to see if there are some interesting results that I might be missing. 

It will be a few days before I can run the grid test, I grid tiles drying right now, but how long do you think I should soak the SCM? 24 hours 36 hours? 48 hours?

I have a friend who does a lot of experimental stuff with glazes I will contact him and see if he has any opinion. 

Catherine Rehbein's work is really nice and colorful, and your right it is glossy and not a sandy matte look like SH's work.

Acids combine with stronitum carbonate to bubble off the carbon dioxide (the carbonate). What you end up with depends on the type of acid used.

Vinegar (acetic acid) creates strontium acetate.  Nitric acid would create strontium nitrate, sulfuric acid strontium sulfate etc.

If Vinegar is strong enough to get the reaction with strontium carbonate going you'll immediately see foaming as you add the vinegar to the strontium carbonate and the carbon dioxide and water vapor bubble off. It should look just it does when you add vinegar to baking soda.

If vinegar is not strong enough to start the chemical reaction on its own, you'll need to heat the mixture over a stove, use a stronger concentration of acetic acid, or more realistically use a stronger acid like hydrochloric acid (called Muriatic Acid at a pool supply store) packing enough energy to break off the CO3 as CO2 and water vapor.

As it sounds like you're new to chemical reactions, always add a strong acid or strong base to the chemical to be added. Never add the chemical to be reacted, in this case strontium nitrate to the strong acid or strong base. This could generate too much heat in that localized area causing the acid or base to boil and splash back at you. Always wear safety glass or goggles. I just picked up 8 of them from Amazon for $2 each for studio members using our new glass saw and glass grinder.

Stuff is real cheap on Amazon as they've recently relaxed the requirements for direct ship from China. Rather than buy a Bohl glass circle cutter for $85 I purchased a nearly identical Chinese version for $5.90, which included the shipping cost from Shenzhen?! Shenzhen is on the border with Hong Kong and is the official exit point for most goods produced through-out China, on their way to the rest of the world.

From memory I think Catherine Rehbein fires her SCM to cone 8, but you'd have to confirm this with her.

I'm not sure what people are looking for here. both Strontium acetate or chloride are bot very soluble in water, so they should be absorbed into the clay body and leave not much in the glaze.

Robert - In my experience Strontium Carbonate doesn't incorporate well into glazes at Cone 6.

There are special Strontium Frits available,  especially used for glazes at Cone 2 and below, but these are quite costly.

I'm actually headed to the studio right now to try vinegar and HCl on strontium carbonate. As for migrating into the bisque, that has benefits as well. Just add more strontium chloride.

I would definitely would like to know what Cone is required to make Strontium Crystal Magic fire like Cathy Rehbein's work. I know from experience it's obviously much hotter than Cone 6 - the same with Jen's Juicy Fruit which is a non-event at Cone 6 oxidation.

Especially given the fact that this is at least nominally a Cone 6 website.

I found kitchen white vinegar easily bubbles off the CO2 from strontium carbonate, making it into strontium acetate which decomposes into Strontium Oxide at 459 F, much lower than Strontium Carbonate - although no one agrees on what that temperature is exactly.

I'm going to try this lower melting strontium in some glazes to see if they look different than the one which use strontium carbonate. The drawback is 43 grams of strontium acetate dissolve in a liter of water, so that will produce a different result as well. I different result I suspect may be quite useful based on the ceramic makers who put strontium frit into their clay bodies.

I've spent a lot of time reworking alleged Cone 6 glazes so they actually fire well at Cone 6. Pete Pinnells Weathered Bronze Green was one of them. Pete says it was originally a Cone 10 glaze and one of his students found it also "worked" at Cone 6. I found "worked" was too subjective and likely the result of an inaccurate kiln temperature which had to have been hotter than the student thought.

Making Weathered Bronze Green into a true Cone 6 glaze required the addition of 20% Ferro Frit 3269. After that addition it looks as beautiful as when it's fired to Cone 10. It only stands to reason it couldn't possibly look the same after firing to Cone 6 without a change in the recipe.

Hi all, been away for awhile.  Some health problems and a major move has taken me out of the game for awhile. Glad to be back.

I fire my work according to an old firing schedule of Steven's which he gave me several years ago.  Basically it fires to cone six, but with the holds and slow cooling the heatwork causes cone nine to bend.  Cone six is flat.  SCM and several other glazes I have work fine at that schedule, but recently I had to switch clay bodies and chose a cone six body... so I have tried to bring the actual firing temp down.  I am finding that SCM and a few other glazes do not melt at the lower temp.  My glazes don't look the same.  I am going back to the beginning and will be testing some alterations.  One thing I wonder is, since Custer Feldspar changed a couple years ago whether it may be altering the glaze.  It was one reason why I had to change clay bodies.   Another factor is that SCM needs to be applied very lightly...if applied thickly it looks unmelted and makes a mess.  Sometimes I draw a pencil mark down the side of a pot (especially porcelain..white on white) so that I can tell when I have sprayed just enough to cover the mark.   I will be sure to report back when/if we find any alternatives.  Peace to all.

I have created a discussion topic about these things we have been talking about.

>> Click here to continue this topic of firing temperature.

Let's move further conversation and test results there. = )

http://kruegerpottery.com/hill-workshop.html

Steven Hill Workshop - St. Louis, Mo.  End of April

Schedule
Day 1 - Friday, April 28, 2017 - 10a - 5p
Steven will throw a few pots, assemble and quick dry them.

Day 2 - Saturday, April 29, 2017 - 10a - 5p
Steven will lecture on spraying and demonstrate the techniques involved. Participants will glaze in the afternoon and we will load the kiln(s) and fire overnight.

Day 3 - Sunday, April 30, 2017 - 10a - 5p
Discussions on spraying techniques and the equipment to set up a spraying studio. Ideas for glaze experimentation after the workshop. Unload kilns and discuss results

$295

Tom

Can anyone explain what the purpose of the second ramp in Steven's schedule is. Why does he go from 220F to 500F at 100F/hour. Every bisque profile I can find goes at a much faster rate of 250-300F. I assume this is a noobie proof schedule so people don't explode pots, but if your preheating for 2-3 hours I can't imagine this makes any sense. I must be missing something! Which is very well possible hah.

John,

I am not really sure either. I am not certain that between 220 and 500F the clay is shrinking that much, is it? Also since the glazes are sprayed I assume they are already pretty dry. The inside being poured could be a reason for this. I am not sure either. I was going to email him about it, but last night I ran a firing with a different ramp of 300F/hour from 220F to 500F. Cutting about 1.5-2 hours from the total firing time. I noticed no differences from before. Nothing exploded, but I know my pots are dry because I preheat them 3 hours during the day then let them sit in the warm kiln until I fire that evening. 

Thanks for the response though. 

Joseph:

I will leave the technical chemistry out of my reply- it puts people asleep. At 270C crystobalite polymorphs can become actual crystals.. Short answer- to stop crystobalite formation.

Tom

Tom,

So do all the other profiles just not care about it. Because every glaze and bisque profile goes faster than 100F. I dont understand I guess. I won't worry about it anymore anyways. Everything came out fine so I am just going to remove the 1+ hour spent there.

Thanks for your answer though.

Joseph

Tom & Joseph -  A several hour pre-heat at 200 F is very effective at thoroughly drying greenware. Some have kilns which cannot easily add this pre-heat so they try other techniques which are not as effective.

On Digitalfire Tony Hansen shows this example of a different firing which quickly heated to 220, above the boiling temperature of water, and held at 220 F for 60 minutes. The temperature then rose again and a bowl with a thick base which was not thoroughly dry exploded. - https://digitalfire.com/4sight/education/firing_what_happens_to_cer...

I call this "case hardening", I'm not sure anyone else does.  By ramping quickly to 220 the exterior of the clay dries and shrinks quickly, mechanically trapping the evaporative water deeper in the ware. So you can attempt to solve the lack of a 200 F pre-heat with a very slow temperature ramp between 220 and 500 F - the range in which mechanically trapped water escapes.

If ware is especially damp it's important to lift the kiln lid during the pre-heat to allow moisture to escape. A tall stack of damp greenware plates or test tiles will see the plates or tiles on the bottom of the stack fire will fire fine, but there will be an increased level of cracking at the top of the pile, because the top ware is soaking in a steam cloud from the ware lower in the stack so doesn't dry completely. 

.

Quartz / cristobalite expansions at this temperature range and inversions as the fired ware cools would not benefit from a slow firing from 220 to 500 F. These 0.8% expansions are affecting tiny particles in the clay with no real effect on the greenware. Cristobalite doesn't form and remain in that state until well above Cone 10, when the silica and clay was formed. I've heard there is additional cristobalite formation above Cone 2, but I have no proof that's the case. Rapid cooling between 500 and 300 F can accentuate any cristabolite shrink problem as these crystals are more structurally incorporated after firing to where the clay is densified.  But cristobalite definitely doesn't form between 220 and 500 F.

Norm,

This makes sense. So I preheat and soak for a good 3-4 hours during the day before my glaze firing at night. I am certain my stuff is dry by then. Thus I can continue to use my 300F/hour to 500F, which makes me save a good 1 hour or more from the 100F/hour to 500F. I never understood that, but that makes sense. He is trying to make sure other people don't explode their ware if they dont preheat sufficiently. 

With a "Cone Fire" digital firing kiln it's easy to add multiple-hour 200 F pre-heat to any firing.

"Kiln Sitter" controllers don't allow you to add a pre-heat to a firing, so people owning those sort of kilns adapted with a slower ramp to 500 F.