holds at end of firing

[grackle]

I keep reading about holding the final temp at the end of firing, but really do not understand how the length of time is chosen.  would like to start adding some small increments of time and see what might change.  any suggestions?  i am thinking start with 5 minutes and more later.  i do sometimes have a few pinholes--but i also notice that some glazes work best in the bottom of the kiln (a bit cooler?)  and some in the top half.   and of course, i do work with different clays--all stoneware, cones 5 and 6.  i do have a vented system--L and L with the air flow.  thank you!!

[Bill Kielb]

I am not a hold person as to me it simply adds heatwork. In a practical sense there are folks who fire one cone lower but add a hold to get to the next cone heatwork without the peak temperature. In that case firing to cone five with a fifteen to twenty minute hold often gets one to cone six. (Usually verified with cones)

Why do that? Some glazes do not like higher peak temperatures. Some underglazes change color significantly with peak temperature. It is a pretty functional way to fire a cone to two cones max higher without hitting the actual peak temperature. 

Firing higher or for longer has never healed pinholes for me, often made them worse. Drop some temperature and hold however has helped on s some of my pinhole situations.

whatever works for you and your desired glaze results is likely the best answer. Whatever is done, I strongly suggest  always nice to have cones in place so you genuinely know how much heatwork was done. As to suggested time, 15-20 minutes generally gets you to the next cone.

Edited January 8 by Bill Kielb

[Mark C.]

I am now a hold the gas kiln at cone 10 for 15 minutes to lessen pitting in rutile reduction glazes -its a life saver right now-I turn the kiln down and adjust damper to keep reduction the same so it does not keep climbing tem wise and the reduction is a constant. Really has helps but it a poain in the butt but worth it right now for me.

[grackle]

Thank you.  I am firing today with a 5 minute hold.  I guess I did not realize that heat would be added, but of course it would.  

[Bill Kielb]

23 hours ago, Mark C. said:

am now a hold the gas kiln at cone 10 for 15 minutes to lessen pitting in rutile reduction glazes

Maybe food for thought - since it’s really hard to maintain temperature and lower the gas as well as shuffle your dampers to maintain reduction this might be a very small / slight drop and hold actually. Especially if you are not significantly dropping the next cone. Maybe an idea to explore - drop and hold pretty popular to heal some pinholes. Might lead to establishing an easier end of firing sequence.

[Kelly in AK]

Tony Hansen enthusiastically champions this idea and has documented it working well for him. I can’t explain what’s happening, but I use it, a drop and hold strategy, and it’s reduced craters and pinholes for me. 30 minutes at 100° below peak temperature. At the same time, I’m constantly navigating other variables that could explain why things work out well or badly, such as adjusting glaze formulas and changing the schedule of reduction in my kiln, so I won’t flat out say it’s a cure all. I have my own peculiar issues. I don’t hesitate to say it’s worth a try. 

[Hulk]

Drop and hold seems to be working/helping in glaze fires for me as well.
I'm also holding in bisque fire, ~1500°F for an hour, powered kiln vent on throughout, which also seems to help.

"Seems" on account of variables, aye.
Some of the clays I've tried are a bit more sensitive to too much heatwork; some are very sensitive to too much heatwork. 

[Roberta12]

1 hour ago, Hulk said:

Drop and hold seems to be working/helping in glaze fires for me as well.
I'm also holding in bisque fire, ~1500°F for an hour, powered kiln vent on throughout, which also seems to help.

"Seems" on account of variables, aye.
Some of the clays I've tried are a bit more sensitive to too much heatwork; some are very sensitive to too much heatwork. 

@HulkWhat is the advantage of a hold on a bisque firing?

[Hulk]

I'd tried extended bisque fire hold (~1500°F) for red, dark brown and black clays I was trying out (a few years ago), where the idea was to thoroughly "burn out" the stuff that will  burn out*. The hold did seem to help with the black clay, however, the main problem I was having with the red clay, fizzy bubbling, was most likely associated with too much heatwork.

I'd set up a powered kiln vent at about the same time.

Any road, my observation (notations were helpful here) was that random pits were greatly reduced in the white, buff, and other red** clays.
My guess there is that random larger bits/chunks of stuff that otherwise wouldn't completely decompose (and hence, produce gas in the glaze fire) in a regular bisque fire get more, or even fully burned out with the hold. I've left the hold in ever since.

I'm fairly sure I got the idea from reading GlazeNerd posts, thanks Nerd!
 

*The black clay, in particular, could bloat where the clay was even a bit thicker.
**I'm using a different vendor's red clay now, which isn't as sensitive to firing over cone five; it also throws better and is less prone to cracking during drying.

[grackle]

Thank everyone, this is a great group!  Just unloaded the kiln with the 5 minute hold, and all looks good.  I was a little worried it might get a bit hot, but seems fine.  I watched the temp right at the end, and it went from 2167F to 2171F, 

I am firing electric to cone 5, but honestly, the witness things would indicate more of a 5.5 or 6.  My first firing with this kiln was a cone 6, and i really felt that it was too hot (colors washed out, etc), so switched to cone 5 with much better results.  I do not see any pitting in this batch.  Tried some different things with stains and clear glaze on white that look good (photo).  Adding a photo of the 4 "horny toads" also known as Texas Horned Lizards.  3 different glazes--slate blue, sage, and  jade.  The jade (most green), is a glaze from my college days, and it has barium carbonate in the mix, so i only use it on non food items.

Giving a good deal of thought to the hold on bisque firing.  I have a black clay that i love, but it is SO messy (turns my hands orange), and tends to blister, but MAYBE if more of the iron or whatever was burned out in the bisque......  I have also experimented with using it as a slip over red clay, and I like some of the results, and will do more with that.

All that said.  I have an L and L kiln with the auto vent system--how do it l Iower the temp for a bisque hold?  I am still learning the menu and I thought I could only HOLD at the final firing temp?

[Hulk]

To drop and hold, the next segment has a lower target temp/target.
Here the rate is maxed at 9999, and the hold is long, three hours (crystal formation), and the final segment is a controlled cool, falling two hundred degrees at the rate of 500°/hour, then holding there for a full hour.

 

For a bisque hold (per prior post, to burn out stubborn organics in thick wares, and/or clays with lots of organic!), I don't believe it matters if the hold is on the way up or down. When running my manual kiln, I held at 1500°F on the way up and down! 
The new kiln, I set the 1500°F hold on the way down.
See "Custom Ceramics Program" in the L&L notebook.

Give a shout if any questions come up?
There are regular members (and Mods) here that are very familiar with writing and editing custom programs.

There are Horned Lizards in California!
Grackle, the figures, how charming, and beautiful glazes, thanks for sharing!

[Morgan]

I can only speak for my glazes and results but after I started doing a small hold at top for 10m (~2190-2200 depending on kiln load), a drop down to 2085 for 30m all of my glaze issues for the most part are good. I seem to get a nicer finish on both matte and glossy with the hold vs just going to peak temp. This is the digital fire drop and soak (no slow cool) schedule and I have never looked back.

[Bill Kielb]

20 hours ago, Morgan said:

~2190-2200 depending on kiln load), a drop down to 2085 for 30m all of my glaze issues for the most part are good

So it looks like you are intentionally firing short of peak cone temp, using a hold at the top to get near to the actual heat work without reaching the actual cone peak temperature and adding a drop and hold for healing? 

[Morgan]

Bill that’s correct. I get a fairly perfect cone 6 bend with that schedule. Every kiln is different obviously and the drop down and hold is for clearing up and healing. 
 

Here is the post on Tony’s site that gives further info:

https://digitalfire.com/schedule/plc6ds

[Bill Kielb]

6 minutes ago, Morgan said:

I get a fairly perfect cone 6 bend with that schedule.

Very cool idea, limit peak temp and get the drop and hold to heal.