Advice for increasing time, decreasing temperature to reach cone 6

[Nancy Talanian]

My rutile blue glaze (Mastering Cone 6, Glossy Base 1, Variegated Blue) hasn't been variegated since I made the switch from an ancient Econo-kiln to an Easy-Fire.  Using records from old firings to program and reprogram the new kiln, I've clearly failed at matching the heat work I achieved with the old Low, Medium, and High settings on my old kiln.  Glaze appears grayish and even instead of bright and variegated.  I assume the difference is that my old kiln with its small elements was relying more on time than on temperature to get cone 6 down.  I'd appreciate any advice for testing that theory without over-firing.   I'm guessing that the second-to-last ramp before cooldown would get the kiln to somewhere between 2000F and 2150 at 100 or so per hour.  Does that sound reasonable?  Can anyone offer an educated guess for the final ramp (speed, target temp., and hold time, if any) to try next?

[neilestrick]

Which firing program have you already tried- one of the Cone Fire settings? Is your new kiln the same size as your old kiln? Have you used cones in your firings in the new kiln to verify that you're reaching the same cone?

[Nancy Talanian]

Hi Neil.  Thanks for responding.  Yes, both kilns are the same size, 23"; old kiln had 2.5" bricks, and new has 3".  I use cone packs on every level.  I've used the suggested program in Mastering Cone 6, the preprogrammed slow glaze to 6, then slow bisque to 6, and probably fast glaze too.  After that I created my own programs with ramps that are a bit wacky in attempting to match what was happening in the Econo-kiln.  For example, after 650, 200/hr to 1200, 350 to 1600, 225 to 1800, 150 to 1900, 200 to 2211 w. 10-minute hold.  I've tested various cooling rates, but that doesn't seem to help, and in the old kiln I never did more than turn all the knobs to medium for 2-3 hrs.

[neilestrick]

200/hr is pretty fast for the last ramp. I'd drop that down to 120F and see how that goes. The cooling could be affecting it, because the new kiln is going to cool slower with the thicker bricks. Is this the same bucket of glaze that you use in the old kiln, or have you mixed a new batch?

[Nancy Talanian]

Thank you again, Neil.  When I made the transition I was using the same bucket of glaze.  I've since mixed several glaze batches, and I've tried different suppliers for the cobalt and copper, and I've also tried both light and dark rutile, so I'm fairly certain it's the firing, not the glaze.  The built-in Slow Glaze program's final ramp is 120/hr. to 2199*, so I guess I've tried it already.  Since you didn't mention it, I assume you don't think my theory about slowing down even more and holding a bit is a solution.

[fergusonjeff]

You might try a faster cooling.  I have some really nice variegated glazes that go matt and bland with a slow cool.  I just crash cool and they come out fine in both my 3 and 10 cubic foot kilns. 

[neilestrick]

If it was glossier before, and more satin now, that could definitely be caused by the slower cooling, especially with rutile in the glaze. Speeding up cooling is a difficult thing, though. Using a downdraft vent will help a little bit, as will packing the kiln looser. Less mass = faster cooling. Beyond that, you're looking at propping the lid at very high temps, which isn't very safe for you or the ware, and wouldn't provide for very even cooling anyway. These 'floating blue' glazes are finicky. I've got a friend who gave up on hers because it started to go more green than blue and she could never fix it.

[Nancy Talanian]

Thank you Jeff and Neil.  Glazes have stayed glossy regardless of the heating and cooling ramps.  Thanks for the suggestion, Jeff, but I've tried both slow cool and uncontrolled cool, and as Neil said, the 3" bricks alone have slowed the cooling from what I was able to do with the Econo-kiln. 

If there are any other suggestions from anyone, I'm all ears, but if not, I'll test the 120 ramp to 2199, or maybe a little slower than that, with a loose pack, and see what happens.  Will report back if I get good results.

[liambesaw]

7 minutes ago, Nancy Talanian said:

Thank you Jeff and Neil.  Glazes have stayed glossy regardless of the heating and cooling ramps.  Thanks for the suggestion, Jeff, but I've tried both slow cool and uncontrolled cool, and as Neil said, the 3" bricks alone have slowed the cooling from what I was able to do with the Econo-kiln. 

If there are any other suggestions from anyone, I'm all ears, but if not, I'll test the 120 ramp to 2199, or maybe a little slower than that, with a loose pack, and see what happens.  Will report back if I get good results.

This happens to me when I fire varigated slate blue or waterfall brown too fast toward the end, I have to have a fully packed kiln to get them to look right.  It's difficult in my manual kiln because switches at medium don't heat it enough but the switches at high heat it too fast.  One high and one medium and the kiln fires unevenly.  I'm working on making a controller for mine to helpfully make the firing process a lot easier, until then I have to pack it full each time. The mug is from a full kiln, the jar is from a firing about half full

[Min]

I'm wondering if it's from a thinner glaze layer. When you are doing your next round of tests I would include some test tiles with double and triple dips (put them on waster cookies in case they run off the test tiles). Has your bisque firing or specific gravity of the glaze changed? Batches of rutile can vary and make a huge difference in some glazes, any change there? Could you post a picture of a pot with the glaze how you want it and how its coming out now?

[Nancy Talanian]

Hi Min.  The change in kilns came within the same batch of glaze, and I was using the same batch of (light) rutile long after that.  Since then I've tried both light and dark rutile but have seen no change.  You are right that the thickness of this glaze makes a difference, but not as much difference as these photos show.  I didn't change the temperature to which I bisque when I changed kilns, but I have been using the Easy-Fire's fast bisque program, which takes a little longer than when I used to turn knobs on my manual kiln.

Thank you, Jeff, Neal, Liam and Min for your help.  This is my first time posting, and it really is wonderful not to be struggling solo in the dark!

[liambesaw]

Wow yeah that has really flattened out, so strange!  I'd go a little bit thicker on the glaze, it looks thinner to me

[Min]

7 hours ago, Nancy Talanian said:

I've used the suggested program in Mastering Cone 6, the preprogrammed slow glaze to 6, then slow bisque to 6, and probably fast glaze too. 

Have you tried a fast glaze firing up to 2000F then 108F up to cone 6 then kiln off (or a short 10 minute soak then off)? To speed up the  kiln cooling down you can run an oscillating or box fan behind it to blow air around the kiln, turn it off when you reach 1200F. Also, try putting a test pot with the proper looking glaze in a bisque firing. If it comes out muddy like the one above I would put it down to too slow a cooling. Just try one change at a time.

[Nancy Talanian]

Thanks Liam and Min.   Min, I really like both of your suggestions.  I'll try what you've suggested in my next bisque.  In the glaze firing, a 10-minute hold/soak could raise the temperature about 1/2 cone, so do you have a suggestion for the target temperature before the hold?  Perhaps 2185?  I could of course watch the cones like in my former, manual-kiln-watching life, but I've not had much success looking through the 3"-deep peepholes in this kiln, so getting the target close would be really helpful.

[Min]

Yes, I would try 2185, might have to fiddle it. I know you're not supposed to do it but what I find helpful for viewing cones is to paint a very thin black line up the length of the cones. (black underglaze) The line really pops out when viewing the cones. I haven't noticed any appreciable difference in the cone bending. (wear kiln glasses)

[Nancy Talanian]

Min, you are brilliant!  Thank you for the suggestion of the lines on the cones.  I'm about to load a bisque, then a glaze firing within the next 7 days.  Will report back afterward.  I really appreciate your help.

[Bill Kielb]

2 hours ago, Nancy Talanian said:

Min, you are brilliant!  Thank you for the suggestion of the lines on the cones.  I'm about to load a bisque, then a glaze firing within the next 7 days.  Will report back afterward.  I really appreciate your help.

This is looking more and more like a composition issue, especially the pictures. Many of these “floating glazes” are mattes that are overmelted a bit to get this look. The original glaze appears less than glossy and appears to have an area at the base of the mug to account for this movement. The new version appears uniform, very glossy with little or no area left in the event the glaze runs. I am Just curious if you have noticed  this diffference. Do you have the recipe? Usually we will see an overmelted matte where the glaze forms as a matte and when slightly over melted the crystals collect and float a bit or move. This does make the glaze relatively sensitive at the end of the firing so some folks devise schedules or holds based on allowing  this movement.

Cones - in the event that the black line is hard to see,  you can use a green dot laser with your goggles and it will light up the cone pack. We use the laser at cone ten where everything is simply red and all color is washed out and in Raku to check when our glazes are fully melted. Only trick is the laser needs to focus from dot to spot and of course be green as red simply disappears in the kiln environment.

short vid on the laser at this link, I think we spent 20 dollars for it.

 

[Nancy Talanian]

Thank you for your insights, Bill.  Although Neil called the glaze a "floating blue," it is Glossy Base 1 from Hesselberth & Roy's Mastering Cone 6 Glazes with "variegated blue" colorants.  http://www.masteringglazes.com/mastering-cone-6-glazes/glaze-reformulations/chapter-6-glaze-reformulati/glossy-base-1-with-g200hp.html I still have the mug, which is as glossy as any pot I've ever seen, so the photographer must have suppressed the sheen to highlight the variegation.  At the bottom and top of the mug are evidence of thin glaze.  Min thought the glaze on the ugly, newer pot might be too thin, but actually the variegation shows best with thinner glaze.  The change in kilns and subsequent loss of variegated appearance happened within the same bucket of glaze.

Thanks also for sharing your laser technique.  I've just painted a set of cone packs using different patterns (thick line, dotted, thin line) to differentiate the temperatures, and I'm firing in oxidation, not reduction, but if the underglaze markings don't suffice, I will look into your laser method.

[Mark C.]

Cone viewing is a learned skill I have found.

[Bill Kielb]

16 minutes ago, Nancy Talanian said:

Thank you for your insights, Bill.  Although Neil called the glaze a "floating blue," it is Glossy Base 1 from Hesselberth & Roy's Mastering Cone 6 Glazes with "variegated blue" colorants.  http://www.masteringglazes.com/mastering-cone-6-glazes/glaze-reformulations/chapter-6-glaze-reformulati/glossy-base-1-with-g200hp.html I still have the mug, which is as glossy as any pot I've ever seen, so the photographer must have suppressed the sheen to highlight the variegation.  At the bottom and top of the mug are evidence of thin glaze.  Min thought the glaze on the ugly, newer pot might be too thin, but actually the variegation shows best with thinner glaze.  The change in kilns and subsequent loss of variegated appearance happened within the same bucket of glaze.

Thanks also for sharing your laser technique.  I've just painted a set of cone packs using different patterns (thick line, dotted, thin line) to differentiate the temperatures, and I'm firing in oxidation, not reduction, but if the underglaze markings don't suffice, I will look into your laser method.

Both samples appear to be porcelain or a light body clay yet the rim on the old mug appears significantly darker. Assuming this glaze works as previously mentioned the darker rim could indicate the presence of more iron. Looking at your recipe aside from the EPK and to a lesser extent the talc your source for iron (as well as titanium) would be dark rutile. Since rutile can vary significantly:

A total wild guess would be to make a recipe or two with varying amounts of Rutile to see if you can regain the level of variation you want and then you could dial in the tone with apportioning that between light and dark.

might be worth trying on a few test tiles, you might find the original and you might find something new you like.

 

[Nancy Talanian]

Thank you again, Bill.  I had always used light rutile, and my supply lasted for a long time.  Since that batch ran out, I've tested both light and dark in 500 gm batches but unfortunately I saw no visible difference.  The recipe also has a lot of RIO as well.  I do appreciate your thoughts, but for now, I've decided to focus on varying the glaze firing, i.e., a slower rise, since my very old Econo-kiln with small elements wasn't capable of rising as easily as my modern one.

[Mark C.]

One word of caution on painting cones-adding colorants can change their melting points. I suggest an unpainted cone next too the painted one to check if they are affected at all?This test would end any worries which I would have if I painted cones

Cones can be affected by getting wet and adding colorants or my to much air blowing on them-all these can affect them.

I have blown air on cones for decades with my mouth only to learn later that this can affect them. They are quite sensitive-check this all out at Ortons web site

[Min]

55 minutes ago, Mark C. said:

One word of caution on painting cones-adding colorants can change their melting points. I suggest an unpainted cone next too the painted one to check if they are affected at all?

Yup, I'm breaking the rules by doing this. With my side by side cone test there was zip difference. Good idea to check though.

[Mark C.]

16 minutes ago, Min said:

Yup, I'm breaking the rules by doing this. With my side by side cone test there was zip difference. Good idea to check though.

Glad you checked-I'm alao breaking the rules as I still blow on cones now and then.I have also tested that as well.

[Dick White]

Nancy, I have an ancient Econo kiln, to which I have added an external controller. I also have a separate thermocouple/pyrometer harnessed to a computer with a logging program with which I can create a minute-by-minute profile of the actual firing performance. I have found that no matter the ramp schedule I program into the controller, the old kiln can only manage around 100F per hour at the very end coming into cone 6.  So, with your new kiln which has the power to actually produce the higher ramp rates of even the "slow" cone fire final ramp, you are firing hotter and faster than before. Knock your final ramp rate down to 100F/hour and watch the cones to decide when to manually turn it off. You'll probably find cone 6 bends at 2175F or maybe even lower. Once you've tuned in the ending temperature, you can incorporate that into the final program segment.