Obvara in same firing as raku

[davidh4976]

At our next raku firing, I'm thinking of trying obvara. Obvara is fired to 1650F while raku fires to 1850F. I'm wondering if I can successfully fire obvara and raku pieces together to 1850F, but allow the obvara to cool before immersion in the obvara fluid. Thoughts? Any idea of what happens if the obvara pieces are hotter than 1650 when dunked?  I thought about using my infrared thermometer gun to read the temperature of the obvara pieces, but it only goes up to 842F, so I can only guess at the temperature of the Obvara pieces.

[Callie Beller Diesel]

So I’m going to preface this by saying I’ve never fired Obvara, and I’ve only ever fired raku by eyeball, never with cones or thermocouple. (Please do this with proper eye protection). So I couldn’t tell you what temperature exactly I was using, but the glaze recipes used were mostly gerstley borate at the time, and that melts between 1550 and 1600 F. 

So my question is, can you fire the raku pieces to a lower temp to match the Obvara recommendations, or are you using glazes that really don’t mature until that hotter temp?

If you do need the hotter temp for raku, it’s possible to roughly judge the temp of a piece by the colour of the glow coming off it.  The  chart linked below has a nice colour gradient illustration, and you can do a bit of a comparison from there. There’s a paywall, but you can use one of your 3 free articles/month to view it. 

https://ceramicartsnetwork.org/ceramic-recipes/recipe/Kiln-Firing-Chart-142658

[davidh4976]

Interesting point. Our raku glazes do best at 1850 or maybe even a bit hotter than that. I typically judge by the look and not so much by the pyrometer, so maybe I can judge the color for obvara...

[neilestrick]

What type of kiln is it? If it has a door, just pull the obvara and then close it up and finish the raku pieces. Otherwise I think you'd probably be fine just firing up to raku temps and pulling the raku pieces first while the obvara cools a bit. It's not an exact temperature anyway, since the pieces cools some between the kiln and the bucket, and the last piece is always a lot cooler than the first.

[PeterH]

On 3/9/2024 at 6:05 PM, davidh4976 said:

so I can only guess at the temperature of the Obvara pieces.

An relevance? https://www.lickinflames.com/obvara_june_2021.html
Generally speaking, the hotter the pot going into the mixture, the darker it will be. Nearly glossy black pots are from the hotter side of the firing range and tan pots are usually from the cooler side of the range. Really hot pots held in the mixture longer will yield fewer patterns. Cooler pots held in the mixture longer will possibly not carbonize as they cool below the threshold where carbonizing can take place.

[davidh4976]

11 hours ago, PeterH said:

An relevance? https://www.lickinflames.com/obvara_june_2021.html
Generally speaking, the hotter the pot going into the mixture, the darker it will be. Nearly glossy black pots are from the hotter side of the firing range and tan pots are usually from the cooler side of the range. Really hot pots held in the mixture longer will yield fewer patterns. Cooler pots held in the mixture longer will possibly not carbonize as they cool below the threshold where carbonizing can take place.

Thanks, that's very useful info!