Strontium Crystal Magic Pitting?

[Erin Noelle]

About 10 years ago, I took several ceramic classes and fell in love with the way Strontium Crystal Magic worked with other glazes. I attached a picture of Strontium Crystal Magic Warm with a spray of Water Color Green that I made in a community college class.

 

Fast forward 10 years and I cannot get anything close to those results. The second picture shows the same glazes with a kiln controller set to a standard medium speed firing schedule to cone 5 with a 12 minute hold time. There are tons of nasty little pin-holes, and although I don't mind the color, it is nothing like I was expecting.

 

The recipe that I copied from San Juan College is as follows:

 

Strontium Crystal Magic

 

Custer Feldspar 2400

Whiting 900

Strontium Carb 660

6 Tile Kaolin 780

3124 Frit 240

Lithium Carb 240

Titanium Dioxide 720

Bentonite 120

 

Total: 6030

Yellow Iron Oxide 121 (2%)

 

Sooo... I noticed online that my SJC recipe has slightly different ratios than the one I found on https://ceramicartsnetwork.org/ceramic-recipes/mid-range/strontium-crystal-magic-warm/. Also, my copy from SJC says "6 tile kaolin" while the one on the website says EPK.

 

Is my recipe written wrong? or is my firing schedule and temperature causing the pin-holing and color difference between the pot 10 years ago and now? I know that glazes are super complicated, but I just don't even know where to start and would really appreciate some help.

 

Thank you for any help!

Erin

 

P.S. I am so sorry the images are huge... I wasn't sure how to re-size them 

 

[Min]

Hi Erin and welcome to the forum. Your glaze recipe is fine, chemistry is nearly identical to the one in the link you posted. Different kaolin but the chemistry is basically the same for both recipes. SCM started out as a high fire Tom Coleman glaze called Yellow Crystal Matte which Steven Hill started using at midrange temperatures and found it worked. I think your blistering problem is to do with the firing schedule you use. Cone 5 plus a 12 minute hold isn't getting you hot enough, I would try a full cone 6.  Also, Hill uses a slow cooling program to develop visual texture in the glazes which also effects the colour of the glazes. 

BTW to make your pictures smaller click on edit then click your picture and a resize screen pops up. Big images are fine too.

[liambesaw]

I believe Steven hill also fires to cone 8.  It's one of those glazes that I have found to be unpredictable, even in the same kiln load.  Like Min said, the cooling cycle is key, those small white crystals (titanium?) On the top picture are from a very slow cooling cycle.  My last tests with SCM had a 5 hour slow cool and hold and I got tons of crystals too.  Might alter that for the next round.  This was fired to a cool 6.

[dhPotter]

Normally SCMC is for cool colors, blues and greens. SCMW is for warm colors, browns, reds. I use both of these glazes extensively. Here is my firing schedule that produces Zero pinholes and a good bit of crystals.

Glaze cone 6...

Segment        Rate F*/HR    Temp    Hold
   1            200         220     30-60
   2            100         500      0
   3            400        2050      0
   4            108        2185^     15
   5           9999        2085     20
   6           9999        1700      0
   7             50        1600     60
   8             50        1500      0

[liambesaw]

9 minutes ago, dhPotter said:

Normally SCMC is for cool colors, blues and greens. SCMW is for warm colors, browns, reds. I use both of these glazes extensively. Here is my firing schedule that produces Zero pinholes and a good bit of crystals.

Glaze cone 6...

Segment        Rate F*/HR    Temp    Hold
   1            200         220     30-60
   2            100         500      0
   3            400        2050      0
   4            108        2185^     15
   5           9999        2085     20
   6           9999        1700      0
   7             50        1600     60
   8             50        1500      0

What are your favorite cover glazes

[dhPotter]

Pete's Seafoam over SCMC - nice light turquoise;  Satin Matte green over SCMC;  Shatz blue Matte over SCMC - goes green and blue depends on thickness;  Bright Sky Blue over SCMC;  Frost Green over SCMC;  Val's Turquoise over SCMC - nice crystals;  Spearmint over SCMC - nice crystals;  Varigated Slate Blue over SCMC - greens and blues depending on thickness. Silky Matte Blue, Tony Hansen's G1214Z base, over SCMC; Carmen Turquoise and Turquoise Satin Matte over SCMC both looked good on Laguna WC607 - looks like crap over WC609 - real dry and rough.

Licorice over SCMW;  Red Orange over SCMW;  Bailey's Red 2 over SCMW;  Waterfall Brown over SCMW - will run;  I have a Butterscotch that really runs when over SCMW but is worth the hassle;  Selsor Temmoku over SCMW - remember Temmoku likes a thick application.

Try any glaze with Strontium Carb over SCM.

Try all your glazes over SCM. It turned all my glazes a lighter shade than the original. I use SCM C or W as spots on the piece to get a highlight of different color from the same glaze.

Steven Hill suggest using SCM up to 40% of the TOTAL glaze thickness. I rarely get it that thick - it will make the cover glaze run. I over applied SCMC then put  Pete's Seafoam over and had a good bit of grinding to do.

 

[glazenerd]

Erin:

your piece from class is on a high iron stoneware body. Copper reacts to iron,  color shifts. The glaze run also indicates higher cone fire. Your new piece is on white stoneware or porcelain ( low-no iron), so that alone will change color. The glaze does not strike me as being mature: need more heat. I know DH fires a lot of SCM, so I would follow his firing schedule. Your pinholes are from potassium by the way: sodium creates much smaller pinholes.

Tom

note: EPK would be the better kaolin: much finer grain than #6- better melt.

[Lbegley]

Steven Hill just had a workshop at the college I lab tech for, and dh's schedule looks right to me (for bisqued work).  I believe Steven does fire to cone 8, but only because he prefers cone 10 clay bodies.  We have fired scm to cone 6 with good results. 

[Joseph Fireborn]

@liambesaw that pot you posted is stunning! I wouldn't change a thing!

[liambesaw]

1 hour ago, Joseph Fireborn said:

@liambesaw that pot you posted is stunning! I wouldn't change a thing!

Thanks! I'm loving it too!

[LeeU]

I have learned the hard way to be grateful for all I have, and to avoid envy, jealousy, and excessive drooling over things or activities that I covet. That said......there is a teeny tiny part of me, buried deep in the dark, that wishes I had done a few things differently, rather than choosing not to commit to, and invest my time, energy, and money in, making clays and glazes, and making things made of clay and treated with glazes.  Gonna leave it at that.  Really appreciate the vicarious pleasure I get from these forums!!!

[liambesaw]

13 minutes ago, LeeU said:

I have learned the hard way to be grateful for all I have, and to avoid envy, jealousy, and excessive drooling over things or activities that I covet. That said......there is a teeny tiny part of me, buried deep in the dark, that wishes I had done a few things differently, rather than choosing not to commit to, and invest my time, energy, and money in, making clays and glazes, and making things made of clay and treated with glazes.  Gonna leave it at that.  Really appreciate the vicarious pleasure I get from these forums!!!

You could always have one of these forum crazies mix up some powder for you and send it off if you wanted to experiment with something like SCM

[dhPotter]

Lbegley the schedule is for raw glazing.

I do not bisque unless I need some calcined EPK. And then the bisqued bowls go right in with the raw glazed ware and glaze fires with the same schedule.

I too took a workshop from Steven Hill 2 years ago. The main difference i see between his schedule and mine,  is  on the downfire, he holds at 1700*F for 60 minutes, I do not.

[CactusPots]

This is essentially Coleman's Yellow Crystal Matte adjusted for cone 6 and substitute strontium for barium?

The SCMW is substantially different than the SCMC over the different glazes?  I'd like to have SCMW adjusted for c10, with barium .  You have given me a few ideas as I use a bit of the YCM over JAC Turquoise (also Coleman).  I don't use in under at all and haven't found a combination I like as much.

[liambesaw]

You can use SCM at cone 10, I think it's actually a cone 10 glaze that works at cone 6 in combination with other glazes.  Don't know if you'll get the same crystallization if you switch it back to barium. You'll have to try

[CactusPots]

The Coleman glaze also doesn't use a frit but 6% GB is the early flux.  It is a running monster that has to be planned for.

Live by the runny glaze die by the runny glaze.

 

 

I will give it a try on my next load as is.

 

[Min]

 

2 hours ago, CactusPots said:

This is essentially Coleman's Yellow Crystal Matte adjusted for cone 6 and substitute strontium for barium?

The SCMW is substantially different than the SCMC over the different glazes?  I'd like to have SCMW adjusted for c10, with barium .

Here you go, the SCM is the version in the link in the first post, the Yellow Crystal Matte recipe is the one from the January 2003 Ceramics Monthly article on Tom and Elaine Coleman. There are some slight differences between the two recipes beyond the source of the boron and strontium sub for barium. 

edit: for anyone who might try the Yellow Crystal Matte recipe it is definitely not intended for food surfaces. Safety Data sheet for barium carbonate.

 

 

[CactusPots]

Let's see here.  This is YCM directly from "With a Little Help from My Friends   Glazes, Clays and Ideas"

The biggest difference I see is that the book recipe has    .50 Zinc Oxide.  i think that help promote crystals. 

I'm more interested in the "warm" version as it has been described as better over brown and black glazes.

Curious that a cone 10 glaze would have a frit.  The GB in the YCM tells me it's going to run like crazy.  It's practically a crystal glaze that needs a catch pot by itself or even over something that's not too stable.

 

[Min]

@CactusPots, those are the "warm" versions of the glaze, I edited my screen shot to include that info.  I not sure that  0.50% zinc oxide is going to make much difference in the crystal formation. The Yellow Crystal Matte recipe was originally fired in reduction, there is some debate if zinc does anything at all in reduction. It might help with forming a catalyst for crystals to form at but I don't think it's necessary for this glaze. If you try it let us know the results with / without the zinc. The ^10 glaze recipe is the one on the right, it doesn't have a frit, sources the boron from the gerstley borate. The ^6 SCM glaze has slightly better silica levels but not by much, still wouldn't be a durable glaze.

[CactusPots]

Min,   Thanks for running the glaze calculator for me.  I haven't messed with that in a long time.  It took me a while to figure out how to read it. 

The YCMW cone 10  never varies more than .2 or .3 % from the original Coleman glaze.  I hadn't thought to try the YCM as an under glaze, only over, so I already have something to try.  Guess I need another batch of test tiles.  This certainly is not a food safe glaze, but holds up the way I'm using it.