Mixing greenware and bisque firing, risk of cross-contamination?

[Annacooley.art]

Hello, please bear with me I'm a relative newcomer to ceramics. 

We have a big kiln.  I want to fire a selection of greenware glazed and unglazed pieces up to 1220 degrees C for a first firing (I'm using black and red grogged stoneware).

I then want to fire the unglazed stoneware pieces again to the lower temp of 1050 degrees C to take an earthenware glaze.  I've done this before no problem.  However, my husband who is a sculptor, has a large (unglazed) greenware piece that he wants to fire in the kiln along with my low-fire glazed pieces in my second firing.  Because the kiln is too big to justify firing it on its own, and it is a commission needed by Christmas.

Neither of us know whether there is likely to be any cross-contamination from my glazes or his greenware.  Can anyone tell me if this will be safe to do?  I have searched other related threads on the forum but I haven't found an answer to my specific problem.

Thank you in advance

 

[oldlady]

i fire to Orton cone 6, in the US.  if your firing temp is about the same, continue reading.   if much hotter, skip it.

depending on the thickness of the sculpture and the other items being close to the same amount, i think you can do this.   my work is usually the same thickness and i have often single fired greenware, plus bisque and refired glazed work at the same time.  usually in a very densely packed kiln.    i have an electronic controller and use the preheat every time.  that means that the firing is very slow.  usually 14 or more hours from switching on to cone 6.   natural cooling takes over 30 hours, i do not slow cool.

if the sculpture is significantly thicker than the other items, do not do it unless someone on the forum with more knowledge tells you something different.

[oldlady]

the only thing i have seen "contaminate" anything was a cobalt blue glaze that spattered a blue circle onto the shelf.  sort of a shadow of blue specks.  i no longer use that glaze.

[2Relaxed]

I've fired a few mixed bisque/low-fire glaze loads in my kiln to cone 04. Even included several glazed greenware pieces a couple of times to single-fire them. It all went fine. I use a pretty long bisque schedule described here: https://ceramicartsnetwork.org/daily/firing-techniques/electric-kiln-firing/bisque-firing-schedule-help-prevent-glaze-faults/  I skip the 12 hour hold because I always make sure my greenware is bone dry. But you might want to include it in the schedule, especially if your husband's sculpture is very thick. Perhaps put it on a lower shelf and nothing else on that level?

[Annacooley.art]

19 hours ago, oldlady said:

i fire to Orton cone 6, in the US.  if your firing temp is about the same, continue reading.   if much hotter, skip it.

depending on the thickness of the sculpture and the other items being close to the same amount, i think you can do this.   my work is usually the same thickness and i have often single fired greenware, plus bisque and refired glazed work at the same time.  usually in a very densely packed kiln.    i have an electronic controller and use the preheat every time.  that means that the firing is very slow.  usually 14 or more hours from switching on to cone 6.   natural cooling takes over 30 hours, i do not slow cool.

if the sculpture is significantly thicker than the other items, do not do it unless someone on the forum with more knowledge tells you something different.

The sculpture is indeed  thicker than my pieces, and different clay body.  I do have an electronic controller and we would do a very slow firing - even so, it seems that the thickness is important... thank you.

[Annacooley.art]

16 hours ago, oldlady said:

the only thing i have seen "contaminate" anything was a cobalt blue glaze that spattered a blue circle onto the shelf.  sort of a shadow of blue specks.  i no longer use that glaze.

Good to know, thank you.

[Annacooley.art]

15 hours ago, 2Relaxed said:

I've fired a few mixed bisque/low-fire glaze loads in my kiln to cone 04. Even included several glazed greenware pieces a couple of times to single-fire them. It all went fine. I use a pretty long bisque schedule described here: https://ceramicartsnetwork.org/daily/firing-techniques/electric-kiln-firing/bisque-firing-schedule-help-prevent-glaze-faults/  I skip the 12 hour hold because I always make sure my greenware is bone dry. But you might want to include it in the schedule, especially if your husband's sculpture is very thick. Perhaps put it on a lower shelf and nothing else on that level?

Thank you that's really helpful.  I'll look up the link you sent