Slow Cooling Of Mixed Glaze Load

[LeeU]

Are there predictable/known problems with firing a program for slow cooling when the load includes a mix of commercial slow cool glazes and commercial regular glazes? Cone 6 electric.

[Joseph Fireborn]

It just depends on how the glazes are formulated. Worst case is the colors will be way off. Turn darker/uglier and dry. Best case they look exactly the same. Middle case they turn matte like in surface.

Only way to know is try it. I wouldn't load a bunch of stuff you care about in a test firing of a slow cool. Do some tiles or test pots you don't care about first.

How slow are we talking?

[Guest JBaymore]

As a BROAD generality.... when you have a molten glaze........ if you fast cool it will tend to be more glossy...and when you slow cool it will have the ability (the time) to allow the precipitation out of the cooling melt of some compounds in the glaze that might be in oversupply.  This is how many matt glazes are made.  It is also how you get the variegation of many glazes surfaces.

 

Slow cooling has more to do with the look of a glaze than what most assume is the "reduction" firing effects in a gas kiln.  Electric kilns are very poorly insulated..... and drop like a rock.  Large sized thick walled and large thermal mass gas kilns cool MUCH more slowly.

 

As Joseph says above...... try it.  But don't risk stuff that MUST turn out like it does in your "normal" cycle.

 

best,

 

.......................john

[glazenerd]

The general temp range that effects glaze the most is 1925-1980F. Crystals, iron spots, matting are at their peak in this range. Slow cooling in general has an effect as noted above; but these temps are the most dramatic. The rate drop will also play a key role. An 300F an hour drop is often used to replicate results of a large kiln firing; in a small test kiln. This rate drop is also used to " heal" glaze issues; which has little effect on glaze finish.

 

Nerd

[Pres]

I fire without a kiln setter or a controller. One of the reasons I bought my kiln new in the 80's that way was so that I could easily fire it up and down. Back  then there were not controllers. I fire down, slow cooling. I find that I get richer depth of color, more visible glaze texture that some would consider crystallization. So for me the kiln reaches  ^6 at 90 degrees, then instead of shutting off, I drop back all switches to 80% until at orange heat. Then drop down to 50% til red then off.

 

Don't know, but it works for me. Of late, I have added a heavier lid, and the firing cycle is needing adjustment as this also slows the cooling.

 

best,

Pres

[LeeU]

THX---will see what shakes out.

[Joseph Fireborn]

Let us know how it goes. I prefer slow cooling, you get some really beautiful results and sometimes really awful results, once you weed through them I think the really beautiful results are worth the time required to let the slow cool run. My total time firing my kiln is around 17 hours right now. That is with no preheat. Most of that is the slow cool and the holds for burnout on the way to cone 6.

 

Every time I try to make it faster I am not happy with the results. 

 

I predict there will be some things you love and some things you don't. You will just have to decide if the things you love about the slow cool are worth the added time and the loss of your other glazes. Since your not formulating your own you can't really modify the glossy glazes to adapt to the slow cool. So you might have to abandon them.

 

Again I don't know how slow you are going, but if its a relatively quick slow cool then I don't think much will change. I always recommend what Neil posted for a beginning slow cool. If I remember right he does 175F / per hour from cone 6 to 1500F. This will give you some variety and not matte over your glossy glazes most of the time.

 

Also make sure you only change one thing at a time! 

[Mark C.]

Slow cooling is where its at for me and gas kiln glaze work. I like a two day cool down. 

I have two cooling now ready to unload after 3.5 days of cooling. I did show one of those days so its a bit longer than usual.

Since I only bisque in electrics I do not care about slow cooling in them.

[Joseph Fireborn]

Slow cooling is where its at for me and gas kiln glaze work. I like a two day cool down. 

I have two cooling now ready to unload after 3.5 days of cooling. I did show one of those days so its a bit longer than usual.

Since I only bisque in electrics I do not care about slow cooling in them.

 

I am curious how fast your kiln drops from the high temps and how long it stays in the middle temps. I imagine you drop from cone 10 to cone 04 decently quick, but then after that I imagine it starts slowing down at an increasing rate? Have you ever recorded it?

[neilestrick]

Slow cooling from the peak temp, rather than letting it drop and then doing the slow cool, will give your glazes a little more time at the hot end of the firing. My glazes like that.

[Mark C.]

 

Slow cooling is where its at for me and gas kiln glaze work. I like a two day cool down. 

I have two cooling now ready to unload after 3.5 days of cooling. I did show one of those days so its a bit longer than usual.

Since I only bisque in electrics I do not care about slow cooling in them.

 

I am curious how fast your kiln drops from the high temps and how long it stays in the middle temps. I imagine you drop from cone 10 to cone 04 decently quick, but then after that I imagine it starts slowing down at an increasing rate? Have you ever recorded it?

 

No I have not.After the 12 hours going up I brick it upon and walk away.

The thermal mass of all the furniture and hard brick in bag walls in the car kiln makes it climb a tad right after shut off and putting in the damper according to the digital pyro.The cool down is slow for awhile  then the longest  time is usually the midrange  to lower temps long after glazes have set. I never fire down my gas kilns.

Crystals have time to grow.

The 8 burners really heat up the floor and bag walls after 12 hours of blasting away.Its a large heat sink as well as the whole load.Unlike electrics where just the load is the heat sink.

[Joseph Fireborn]

 

 

Slow cooling is where its at for me and gas kiln glaze work. I like a two day cool down. 

I have two cooling now ready to unload after 3.5 days of cooling. I did show one of those days so its a bit longer than usual.

Since I only bisque in electrics I do not care about slow cooling in them.

 

I am curious how fast your kiln drops from the high temps and how long it stays in the middle temps. I imagine you drop from cone 10 to cone 04 decently quick, but then after that I imagine it starts slowing down at an increasing rate? Have you ever recorded it?

 

No I have not.After the 12 hours going up I brick it upon and walk away.

The thermal mass of all the furniture and hard brick in bag walls in the car kiln makes it climb a tad right after shut off and putting in the damper according to the digital pyro.The cool down is slow for awhile  then the longest  time is usually the midrange  to lower temps long after glazes have set. I never fire down my gas kilns.

Crystals have time to grow.

The 8 burners really heat up the floor and bag walls after 12 hours of blasting away.Its a large heat sink as well as the whole load.Unlike electrics where just the load is the heat sink.

 

 

Thanks for the reply. It is all so interesting.