Comparison Of Slow & Fast Cooled Iron Reds.

[John255]

This thread is directed toward those ^6 potters who have an interest in Iron Red glazes but have manually controlled kilns that do not easily allow soaking and extended cooling.

The slow cooled samples were fired in a 1.5 cu.ft., computer controlled test kiln using Steven Hill's firing schedule for bisque ware. Essentially, this was slow up and down with a one hour hold when ^6 went over and another hour at 1600F. The fast cool firing was done by a friend in a 3.5 cu.ft. Jen-Kiln with 3" bricks, using only the Dawson sitter with no soaking, no pyrometer, and no extended cooling. Self-supporting witness cones were used in both firings.

The glaze formula was Bailey's Red: Custer 47%, EPK 4%, Bentonite 2%, Bone Ash 15%, Lithium Carb. 4%, Talc 17%, Silica 11%= 100%. Plus a short line blend of 12%, 15%, and 20% Spanish Red Iron Oxide (SRiO). All samples were dipped in the same glaze bucket.

Observations:

Photo one shows a greater red color difference between 12%, and 15% SRiO than the difference between slow and fast cooling. Although the slow 12.5 hour firing did promote slightly more red the 7.5 hour fast cooled samples had more textured pattern, and by my opinion were more desirable. This was especially true for the 15% sample where there was a lot of gold speckling. I'm not sure what this is, but I've heard it called "pyrite." My supplier list Spanish Red Iron Oxide as 80% FeO3. Although there are many variables in a test like this the one that seems most important is the quality and quantity of iron used.

Photo two shows larger samples of 3.5" high yunomi's, with same Bailey's glaze at 20%. The slow cooled was very smooth, more toward kaki color, and wonderful to the touch. Once again there was more pattern in the fast cooling. I'm also experimenting with Steven Hill's Strontium Crystal Magic glazes so will continue to fire my iron reds slow. Hope this post is handy for some of you who may have thought iron reds were not for you.

Regards,

John255
 

[Roberta12]

This thread is directed toward those ^6 potters who have an interest in Iron Red glazes but have manually controlled kilns that do not easily allow soaking and extended cooling.

 

The slow cooled samples were fired in a 1.5 cu.ft., computer controlled test kiln using Steven Hill's firing schedule for bisque ware. Essentially, this was slow up and down with a one hour hold when ^6 went over and another hour at 1600F. The fast cool firing was done by a friend in a 3.5 cu.ft. Jen-Kiln with 3" bricks, using only the Dawson sitter with no soaking, no pyrometer, and no extended cooling. Self-supporting witness cones were used in both firings.

 

The glaze formula was Bailey's Red: Custer 47%, EPK 4%, Bentonite 2%, Bone Ash 15%, Lithium Carb. 4%, Talc 17%, Silica 11%= 100%. Plus a short line blend of 12%, 15%, and 20% Spanish Red Iron Oxide (SRiO). All samples were dipped in the same glaze bucket.

 

Observations:

 

Photo one shows a greater red color difference between 12%, and 15% SRiO than the difference between slow and fast cooling. Although the slow 12.5 hour firing did promote slightly more red the 7.5 hour fast cooled samples had more textured pattern, and by my opinion were more desirable. This was especially true for the 15% sample where there was a lot of gold speckling. I'm not sure what this is, but I've heard it called "pyrite." My supplier list Spanish Red Iron Oxide as 80% FeO3. Although there are many variables in a test like this the one that seems most important is the quality and quantity of iron used.

 

Photo two shows larger samples of 3.5" high yunomi's, with same Bailey's glaze at 20%. The slow cooled was very smooth, more toward kaki color, and wonderful to the touch. Once again there was more pattern in the fast cooling. I'm also experimenting with Steven Hill's Strontium Crystal Magic glazes so will continue to fire my iron reds slow. Hope this post is handy for some of you who may have thought iron reds were not for you.

 

Regards,

 

John255

 

 

 

I am soooo impressed! I was using different red recipes....some from Michael Bailey's book, some from another place and programmed in a slow cool and everything was brown brown brown. I am going back to the drawing board! Thanks for the great pictures!

 

Roberta

[John255]

OK.Good luck Roberta.

Let us know how you make out.

Regards,

John255

[Denice]

John you'll have fun testing iron red glazes over the SCM, I fired a load of coil built gourd shape pots they all came out fantastic. I used the warm tone SCM I have read about a cool tone SCM, I didn't use Bailey Red I used misc glazes that I had that I had already mixed, two of them were Iron saturates. I did test first just to make sure I wouldn't have any major diasters. Denice

[OffCenter]

For blues, greens SCM cool usually works better than SCM warm but for most other glazes the warm seems better. At least, that has been my experience with using them. I don't have much luck with Bailey's Red but I do get nice reddish-golds with Juicy Fruit. I changed it from RIO to Spanish Iron Oxide. Hill recommends SCM amount to about 60% of the thickness of it and the glaze on top, but for this one the SCM warm should be thinner than the Spanish Juicy Fruit but neither extra thick.

 

Neph Sy ... 43.6

Silica ... 10.7

Whiting ... 9.8

EPK ... 8.9

Frit 3124 ... 8.0

Lithium Carb ... 8.0

Soda Ash ... 8.9

Bent ... 2.0

Spanish RIO ... 7.2

 

Jim

[Min]

Terrific results John, thanks for posting. Your pictures are very well done, any tips on taking such good photos?

 

Min

[Chris Campbell]

I have to comment here that the difference in the firings is a lot more than just the cooling rate.

 

Heatwork. The one hour hold took that firing way over Cone 6 to at least 7 or 8.

Holding at six doesn't mean the firing just sits at Cone 6 .... Firing temps are a combination of time and temp.

Think of holding your perfectly roasted chicken in the oven for an hour longer at 350 ... Different result ... no matter how you cool it.

[Marcia Selsor]

I use the matts from Baileys book and the Bailey's red. It has to be on just the right thickness

as well as the firing and cooling to come out a good red and not brown.

Soaking helps. I haven't increased the iron content. I think it is already pretty high at 11%

 

Marcia

[OffCenter]

I have to comment here that the difference in the firings is a lot more than just the cooling rate.

 

Heatwork. The one hour hold took that firing way over Cone 6 to at least 7 or 8.

Holding at six doesn't mean the firing just sits at Cone 6 .... Firing temps are a combination of time and temp.

Think of holding your perfectly roasted chicken in the oven for an hour longer at 350 ... Different result ... no matter how you cool it.

 

I think most people working with SCM and iron saturates are aware of that and when using a computer set the peak temp below what is usually listed as the temp at which cone 6 falls so that the hold results in a cone 6-7 firing instead of a 7-8. Also, I've learned when I first started experimenting with controlled cool downs that with some (not all) iron saturates you can get the same or better results simply firing a cone 6 glaze to cone 7 or 8 instead of doing a complicated cool-down. Just straight firing as fast as the kiln will go to 7 1/2 and then uncontrolled cool down. Sure a lot less wear on the kiln.

 

Jim

[Min]

I have to comment here that the difference in the firings is a lot more than just the cooling rate.

 

Heatwork. The one hour hold took that firing way over Cone 6 to at least 7 or 8.

Holding at six doesn't mean the firing just sits at Cone 6 .... Firing temps are a combination of time and temp.

Think of holding your perfectly roasted chicken in the oven for an hour longer at 350 ... Different result ... no matter how you cool it.

 

 

I think most people working with SCM and iron saturates are aware of that and when using a computer set the peak temp below what is usually listed as the temp at which cone 6 falls so that the hold results in a cone 6-7 firing instead of a 7-8. Also, I've learned when I first started experimenting with controlled cool downs that with some (not all) iron saturates you can get the same or better results simply firing a cone 6 glaze to cone 7 or 8 instead of doing a complicated cool-down. Just straight firing as fast as the kiln will go to 7 1/2 and then uncontrolled cool down. Sure a lot less wear on the kiln.

 

Jim

 

Ditto what Jim said. My kiln takes about 2 days to cool down to 300F, mass is the other factor.

[Chris Campbell]

I think most people working with SCM and iron saturates are aware of that and when using a computer set the peak temp below what is usually listed as the temp at which cone 6 falls so that the hold results in a cone 6-7 firing instead of a 7-8.

 

Even the firing experts would not be able to say with authority where the kiln was after a hold of any length.

Sure, potters guess at it and repeat successful experiments ... but it is not science yet.

I would say that a one hour hold boosts that temp a lot higher than one cone. I get two cones with a fifteen minute hold.

[John255]

Terrific results John, thanks for posting. Your pictures are very well done, any tips on taking such good photos?

Min

 

 

Thank you Min for the compliments.

I use the KISS philosophy these days for photography. Of my six digital cameras my favorite is an entry level Canon A480 $80.

Background are poster boards from Walmart $.69 in various colors. For the test tiles the on-board flash was used.

I use PhotoShop Elements and 6~7 other photo editing apps, some with only one good feature. Tere are many out there, some free.

The test tiles are cropped and copied to the clip-board then pasted on a black background. Annotation is then applied.

Since this is a bit OT we can PM more detail if you are interested.

Regards,

John255

 

 

 

 

 

[John255]

 

 

I have to comment here that the difference in the firings is a lot more than just the cooling rate.

Heatwork. The one hour hold took that firing way over Cone 6 to at least 7 or 8.
Holding at six doesn't mean the firing just sits at Cone 6 .... Firing temps are a combination of time and temp.
Think of holding your perfectly roasted chicken in the oven for an hour longer at 350 ... Different result ... no matter how you cool it.

We really didn't need the basic lecture on heat-work. The essential message of this thread is the quality and quantity of iron, for this batch of Baileys Red, had more visible red effect than soaking and slow cooling with approximately the same heat-work for both firings. This may be exciting news for folks with older kilns who have been told "Slow cooling is an absolute must, or the only way to get iron reds."
Regards,
John255

 

[John255]

I use the matts from Baileys book and the Bailey's red. It has to be on just the right thickness

as well as the firing and cooling to come out a good red and not brown.

Soaking helps. I haven't increased the iron content. I think it is already pretty high at 11%

 

Marcia

 

 

Marcia,

I'm sure you are right about the thickness. I tried to have that as close as possible for both samples.

However, it will always be one of the countless variables we deal with.

Yes, the iron is high if you believe all iron is 100% FeO3.

Obviously this is not so, and my future use of different irons will include a line-blend.

Thanks.

John255

[John255]

I have to comment here that the difference in the firings is a lot more than just the cooling rate.

 

Heatwork. The one hour hold took that firing way over Cone 6 to at least 7 or 8.

Holding at six doesn't mean the firing just sits at Cone 6 .... Firing temps are a combination of time and temp.

Think of holding your perfectly roasted chicken in the oven for an hour longer at 350 ... Different result ... no matter how you cool it.

 

 

I think most people working with SCM and iron saturates are aware of that and when using a computer set the peak temp below what is usually listed as the temp at which cone 6 falls so that the hold results in a cone 6-7 firing instead of a 7-8. Also, I've learned when I first started experimenting with controlled cool downs that with some (not all) iron saturates you can get the same or better results simply firing a cone 6 glaze to cone 7 or 8 instead of doing a complicated cool-down. Just straight firing as fast as the kiln will go to 7 1/2 and then uncontrolled cool down. Sure a lot less wear on the kiln.

 

Jim

 

 

Equating wear and tear and cost of firing against the degree of visible results is an excellent point Jim.

John255

[Denice]

John keep us informed about your upcoming test, I have had some heat soak issues and have been experimenting with different soaking times and temperature. Unfortunately my test kiln is too small and cools down to fast for any of these test. My two larger kilns are 25 and 40 years old so I am using the Skutt dual pryometer set up to determine the temp and manually adjust the temp on the kiln. I appreciate any info you come up with. Denice

[John255]

John keep us informed about your upcoming test, I have had some heat soak issues and have been experimenting with different soaking times and temperature. Unfortunately my test kiln is too small and cools down to fast for any of these test. My two larger kilns are 25 and 40 years old so I am using the Skutt dual pryometer set up to determine the temp and manually adjust the temp on the kiln. I appreciate any info you come up with. Denice

 

 

OK Denice you can bet I will post anything of interest.

Thanks.

John255

[Chris Campbell]

I have to comment here that the difference in the firings is a lot more than just the cooling rate.

 

Heatwork. The one hour hold took that firing way over Cone 6 to at least 7 or 8.

Holding at six doesn't mean the firing just sits at Cone 6 .... Firing temps are a combination of time and temp.

Think of holding your perfectly roasted chicken in the oven for an hour longer at 350 ... Different result ... no matter how you cool it.

 

 

We really didn't need the basic lecture on heat-work. The essential message of this thread is the quality and quantity of iron, for this batch of Baileys Red, had more visible red effect than soaking and slow cooling with approximately the same heat-work for both firings. This may be exciting news for folks with older kilns who have been told "Slow cooling is an absolute must, or the only way to get iron reds."

Regards,

John255

 

 

I swear I don't mean to be argumentative ... so please educate me because those two firings seem worlds apart to me. I cannot come close to understanding how the two could possibly have the same amount of heat work and I am not referring to basic heat work 101 when I ask this. I am referring to the fact that heat work continues through a hold.

 

If you want to say that you are comparing two ways of firing the same glaze, I get that.

[OffCenter]

I think most people working with SCM and iron saturates are aware of that and when using a computer set the peak temp below what is usually listed as the temp at which cone 6 falls so that the hold results in a cone 6-7 firing instead of a 7-8.

 

Even the firing experts would not be able to say with authority where the kiln was after a hold of any length.

Sure, potters guess at it and repeat successful experiments ... but it is not science yet.

I would say that a one hour hold boosts that temp a lot higher than one cone. I get two cones with a fifteen minute hold.

 

 

Sorry, Chris, but I don't get your point. It's just not a big deal to estimate how much to drop the peak temp to compensate for slow ramps and holds and fine tune it with one or two more firings. Tweaking the ramps and holds on a computerized elect kiln is just like the tweaking you do when you fire a wood kiln, salt kiln, reduction kiln, raku kiln, etc.

 

Jim

[Chris Campbell]

Well ... I have had a hard time learning about firing and trying to understand the technical side and I thought I had a tentative grasp ( finally ) on what heat work was and how it affected firing results.

So when a potter with 34 years experience ... As John has ... Says these two firings had the same heatwork, it throws me back to square one of thinking I don't understand at all.

[OffCenter]

Well ... I have had a hard time learning about firing and trying to understand the technical side and I thought I had a tentative grasp ( finally ) on what heat work was and how it affected firing results.

So when a potter with 34 years experience ... As John has ... Says these two firings had the same heatwork, it throws me back to square one of thinking I don't understand at all.

 

 

You probably understand as much or more than most of us. It's all more art than science and as Jesus said, "Heatwork is heatwork."

 

Jim

[John255]

I have to comment here that the difference in the firings is a lot more than just the cooling rate.

 

Heatwork. The one hour hold took that firing way over Cone 6 to at least 7 or 8.

Holding at six doesn't mean the firing just sits at Cone 6 .... Firing temps are a combination of time and temp.

Think of holding your perfectly roasted chicken in the oven for an hour longer at 350 ... Different result ... no matter how you cool it.

 

 

We really didn't need the basic lecture on heat-work. The essential message of this thread is the quality and quantity of iron, for this batch of Baileys Red, had more visible red effect than soaking and slow cooling with approximately the same heat-work for both firings. This may be exciting news for folks with older kilns who have been told "Slow cooling is an absolute must, or the only way to get iron reds."

Regards,

John255

 

 

I swear I don't mean to be argumentative ... so please educate me because those two firings seem worlds apart to me. I cannot come close to understanding how the two could possibly have the same amount of heat work and I am not referring to basic heat work 101 when I ask this. I am referring to the fact that heat work continues through a hold.

 

If you want to say that you are comparing two ways of firing the same glaze, I get that.

 

 

Christ,

Yes that is exactly right, "the two firings are worlds apart." On the forums, and is some literature It is an accepted theory that the only way you can get iron red instead of brown is to use slow cooling. One firing is controlled with ramps and soaks and the other is not. Both firings did produced iron reds. The cones are included in the photos to show neither kiln was over, or under fired at cone 6. My hope is that the test can be repeated by those with older kilns. That's all I wanted to show. The discussion got off on SCM concerns that many are interested in. In an effort to keep it simple I'm sorry I did not explain it well enough. Your understanding of heat-work is probably OK.

John255

 

 

[Chris Campbell]

Thanks for the explanation.

I appreciate it since I have never fired iron red glazes ... amazing actually that I have spared myself any frustrating clay experience.

[John255]

Thanks for the explanation.

I appreciate it since I have never fired iron red glazes ... amazing actually that I have spared myself any frustrating clay experience.

 

 

OK Chris, sounds like you are on track now.

I just looked at your work and find it absolutely gorgeous.

I have no idea how you do that.

It's far beyond anything I could do.

Regards,

John255

[Chris Campbell]

Thanks John ... finding the proper niche for firing that work successfully is what has me so interested in heatwork, ramping, cooling etc. Controlled cooling has cut my loses by at least half but I think controlling the actual heatwork will go even further with this.

 

At the last NCECA there was an excellent presentation on the future of firing and heatwork. Ever since we potters got computers on our kilns and started playing with them, the importance of knowing the real heatwork is going up. Most of what they were saying went over my head, but once they started showing pictures I began to get it and it was exciting and fascinating. This is just early days though and there is a lot more research to be done.