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Posted by Bubbles_ on September 26, 2007, 6:39 pm
Please log in for more thread options Hey again
Sorry you aren't feeling well! Get well soon!
I think it is "bear" - as in to bear a burden, not the animal - hehe!
Okay - I haven't even seen anyone using cones over here in Europe - my
teacher doesn't even with her new kiln, and neither did an old teacher of
mine. I can't remember seeing any in the extensive catalogue from my dealer,
either.
I was told that sponging off bisque-ware was only to remove the dust. My
workshop typically has a humidity of around 50 %. I guess maybe that should
be enough.
But, when you mention during glazing, I do sometimes se that just little
spots aren't covered - like a little speck of grog. I just dab it with my
brush with glaze on it, but could that be part of the problem? I like your
suggestion of a little quick dip in water, and will try that later on. I
need to get myself one of those potter's pencils that doesn't burn away -
and start numbering my pots and writing down their whole way through the
processes.
The clay I use is this:
http://www.michel.ch/michel/katalog/ton_tony.asp?Redirect=True
Apollo Steinzeugton 1000 - 1300°C
weiss - hellcrème - hellgrau
Westerwälder Steinzeugton ( WM2502 ), sehr fein schamottiert
Hervorragender Drehton, sehr plastisch, gute Standfestigkeit, auch für sehr
grosse Stücke. Einfach und gut im Trocknen. Guter Glasurträger. Raku
möglich.
Technische Daten
Rohbrand 950 - 980°C
Brennbereich 1000 - 1300°C
Sintertemperatur 1220°C
Brennfarbe weiss - hellcrème - hellgrau
Schamottierung 25 % 0 - 0.2 mm
Trockenschwindung 5 %
1000°C 1100°C 1200°C 1260°C
Brennschwindung 0.5 % 3 % 5 %
Wasseraufnahme 14 % 9 % 3 %
WAK ( 20 - 500 °C ) 7.2
I'm stuck on translating any of this at the moment, but will try if you
don't get the general gist of it.
These are the glazes I use.
http://www.michel.ch/michel/katalog/glasur_1250.asp?Redirect=True
The one I have most problems with at the moment is 101 with a glaze improver
over. The improver - number 100 - makes it go different blues and greens and
blacks when I add it on top. Fantastic colors, but the bubbles keep showing
up. Mind you, I had a bubble on a matte glaze - 404, I think - on this last
high firing. I don't have this problem at all with low-fire stuff - at 1050
C, same as my bisques (that way I can mix them a bit and get a full kiln
faster).
My kiln is teeny - only about 2 feet wide and maybe 3 feet tall inside - so
I wouldn't expect huge temperature ranges inside except when firing with the
holes open - on in the lid, one right down at the bottom. possibly even
below the bottom shelf. I open those about up to 650 then close them. I
can't remember any bubbly piece specifically being by the open holes, and
glazes only really start to melt well above 650C, don't they?
I'm going to go fire my kiln now. It is a bisque, and I will check my glazes
to see if they can be fired higher than 1050 - there are a couple I have
that shouldn't be, which is why I have stayed at that temp, and I have some
glazed stuff going in now.
Thanks again for your time and input!
***virtual chicken soup for you to get better on***
Marianne
> Hi Marianne!
>
> I'm home sick with flu and not functioning 100% so bare (or is that bear)
> with me...
>
> First, you should use cones on all firings or at least do regular spot
> checks. You need to know what heat work you are getting not just what
> temperature you are going to and you need to know that for different spots
> of your kiln.
>
> You can try bisque firing to cone 04 (1060 C). I only fire to 06 (995 C)
> and have no problems but I mix my own glazes and know the materials I am
> working with. Firing to 04 is often recommended. Do you make up your own
> glazes or are you buying glazes? If you don't fire with cones, see if you
> can beg, borrow or steal some until you can buy your own, at least to
> check your next bisque firing.
>
> You can get bubbles before if your pot is very, very dry when glazing. I
> am one of the few potters out on the eastcoast that I know of who rinses
> off their bisqueware before glazing. It is a really, really quick rinse
> so the pots are still absorbant. I was taught in the desert environment
> where it was so dry you could soak your bisqueware in water and five
> minutes later they would be bone dry. In fact you had to dip them in
> water or the glaze bubbled up. You can wipe down your pots with a damp
> sponge to both clean them off and decrease bubbling on the dry glaze
> surface. This is probably not the problem with your glaze however. It is
> something you would notice by now.
>
> Let us know about the glazes you use. (if you mix your own, what
> ingredients - better yet what recipe are you using).
>
>> Hi DKat! Good to see you!
>>
>> I am firing bisque to 1050 C.
>>
>> It usually happens with the really glossy glazes, but I actually had one
>> bubble on a matte glaze this time as well.
>>
>> Since the bubbles go all the way in to the clay, do you think I might be
>> bisque firing too low, so that there are "substances" left in the clay
>> before the glaze firing?
>>
>> I do think my oven's thermometer might show a bit higher than it actually
>> is, so maybe just increasing to 1060 or 1070 would help?
>>
>> Once again - any input greatly appreciated! Especially since I have a
>> full load for bisque firing ready.
>>
>> Marianne
>>
>>
>>
>>> How high are you bisque firing to? What glaze is this happening with
>>> (is it all glazes, just one, a mix)? We need to know more before
>>> suggestions would be of much use. 40 minutes of hold time is way more
>>> than you should need so something is not as it should be.
>>>
>>>
>>>> EWWWW!!
>>>>
>>>> I keep getting bubbles on my finished pieces. I have tried up to 40
>>>> minutes hold time at 1270 degreess, but they still show up! I am
>>>> getting rather frustrated by it all. I can "repair" them by adding
>>>> glaze to the holes (that are more like inverted craters going all the
>>>> way down to the clay) and refiring once or even twice, but I have a
>>>> very small kiln at home, and find it both a waste of space and power,
>>>> while at the same time not wanting to "lose" the pieces.
>>>>
>>>> Any ideas on other things I could try? Last kiln was 6 hours to 650,
>>>> then up to 1270 and hold for 30 minutes. The cooling was over almost a
>>>> day. Policy being that over about 400, I don't even let the cool air of
>>>> the laundry room in, but after that, I take out a couple of plugs (top
>>>> center and bottom) and under 200 I start opening the lid of the kiln a
>>>> little. That shouldn't affect the bubbles, though, as I am sure they
>>>> have set at much higher temperatures.
>>>>
>>>> BUT - AGH!!!
>>>>
>>>> Any input and suggestions greatly appreciated!!!
>>>>
>>>> Marianne
>>>>
>>>
>>>
>>
>>
>
>
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