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VladCruceanu

Glaze on bonsai pot foot

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Hi guys,

I am just starting with pottery and glazes, finding it extremely interesting. In the past weeks I built a couple of bonsai pots, 2 of them being bisque fired. Stoneware was used.

Next step in my journey is to glaze them. I bought 2 brush-on glazes and in the following days I want to start the work.

My questions are the following:

1. I know that I am not supposed to glaze the pot foots because the glaze will stick to the kiln. I should apply wax resist on the entire foot or just on the part that will actually sit on the kiln? I saw pots that have the foots glazed, the lateral parts. How can this be achieved? Attached you will find an example.

2. The kiln owner is high-firing only for me because he usually is low firing kids items, so the cost is pretty high for me as I have to pay for the whole kiln every time. If I will glaze the 2 pots now, can I keep them safe and fire them in 2-3 weeks when I will have a couple of other pots made so I can pay for the whole kiln and have several items fired? Is there any issue if I'm firing glazed pots for the second time and bone dry for bisque fire, everything works at same temperature of 1.280 C?

Thank you.

Vlad

03.19.2018_Web_Store-129_1080x.jpg

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Are you glazing pots  which have not been fired at all?

If you know you have stable non runny glazes it is possible to glaze very close to where foot touches kiln shelf.

Can be fired with small tiles of clay under each foot so any runs are caught and can be ground off.

Glazed pots can be kept till you have an entire kiln full.

Protection from dust and moisture. Care when handling.

Everything doesn' work at same temp.

You could get your pots bisque, lower temp, when he bisque the kids stuff

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The pots I want to glaze are bisque fired. As this is the first time using these glazes, I don't know if are runny or not, I will find out soon.

Thank you for the idea of how to glaze the foots. In terms of design, it might look better for my pots to leave the foots unglazed. I will think about it.

The stoneware clay I have is recommended to be fired at 1,280 C and my glazes at the same temperature. So the temperature is the same but I don't know if the heating curve of the kiln can be the same if I will fire 2 pots for glazing and another 2 pots for bisque. This way it will be more cost effective. 

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If you fire to that temp your pots which start raw will need gentler rise till about 700deg. Celsius but if taken up to 1280  will not accept the glaze as will be very unporous . This slow rise to 700 is what raw to bisque needs.

A bisque of about 1000deg C or a little higher is the norm for attaining enough porosity to let good glaze application occur.

Better to be patient,  get enough bisque pots Then fire  your glazed pots..if don' t know glazes and not your kiln I would be placing my pots on bisque discs of clay to protect the kiln shelves and also your pots. Will be more expensive to pay for spoiled shelves!

Get potting!

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You can't bisque to 1280C. The pots will be vitrified and won't take glaze.

I wouldn't even worry about wax on the feet since you're brushing on the glazes. If any gets on the bottom of the feet, just sponge it off. Make sure the glaze is a few millimeters from the bottom of the foot. You need a little space for the glaze to run. If cost is an issue, I would get as many pieces as you can bisqued and glazed to fire at one time. It might also be worth the money to fire a couple of tests of your glazes before putting them on a bunch of pots.

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23 minutes ago, neilestrick said:

You can't bisque to 1280C. The pots will be vitrified and won't take glaze.

I wouldn't even worry about wax on the feet since you're brushing on the glazes. If any gets on the bottom of the feet, just sponge it off. Make sure the glaze is a few millimeters from the bottom of the foot. You need a little space for the glaze to run. If cost is an issue, I would get as many pieces as you can bisqued and glazed to fire at one time. It might also be worth the money to fire a couple of tests of your glazes before putting them on a bunch of pots.

So when it writes on my stoneware clay 1,280 C, it means that I can bisque fire to a lower temperature and after I glaze, I should fire at 1,280 C?

My glazes are for high temperature, one is for 1,200 - 1,240 C and one for cone5, that means around 1,050 C if I remember correctly. 

I glazed both my pots and the glaze stays very well on the pots. Should I have any firing issues?

Thank you.

 

 

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Yes, you need to bisque at low fire temps- cone 04- and glaze at whatever cone your glazes mature at. If your clay fires to cone 10 but your glaze goes to cone 5, then you have to fire to cone 5. The problem with that scenario is that your clay will not be fully matured, and may weep moisture if the glaze isn't perfect. Any crazing in the glaze and water can seep into the clay and weep out the foot. Ideally, you want to get a clay that is fully matured at cone 5, like your glaze. I recommend not firing at cone 9 or 10 in an electric kiln because it will really put a lot of wear and tear on the elements and bricks. Cone 5 or 6  is much easier on the kiln.

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1 hour ago, neilestrick said:

Yes, you need to bisque at low fire temps- cone 04- and glaze at whatever cone your glazes mature at. If your clay fires to cone 10 but your glaze goes to cone 5, then you have to fire to cone 5. The problem with that scenario is that your clay will not be fully matured, and may weep moisture if the glaze isn't perfect. Any crazing in the glaze and water can seep into the clay and weep out the foot. Ideally, you want to get a clay that is fully matured at cone 5, like your glaze. I recommend not firing at cone 9 or 10 in an electric kiln because it will really put a lot of wear and tear on the elements and bricks. Cone 5 or 6  is much easier on the kiln.

When I am having a glaze that should be fired to a lower temperature than the one at my clay matures, can I bisque fire at the clay maturing temperature, and after that glaze it and fired to a lower temperature?

@neilestrick is saying that because I fired at 1,280 C, as was indicated for my clay, now it is vitrified and it cannot be glazed, as it is not porous. But my glaze is on the pot, in 4 coats and looks great. I will try to fire it tomorrow and see what is happening. 

 

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Well if you've put any cone 5 glaze on that pot  it will certainly run at cone 10 so if I was the kiln owner I would not let it near my kiln

Bisque fired ware as Neil wrote is fired at a low temperature so it accepts glaze application.

You CAN fire your clay to whatever temp you want but it will only vitrify at around temp stated by maker.

Lower will give it a higher rate of absorption so in bonsai pot water will be absorbed and evaporate if clay is fired lower than recommended.

May not matter for bonsai I don' know but would matter for coffee mug.

Bisque ware is deliberately fired to lower temp.

Glaze ware is deliberately fired to a certain temp ...to mature glaze and to vitrify clay to the degree required for its function.

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Long story short, 2 weeks ago I went to the kiln owner for bisque firing and after he discussed with the kiln manufacturer, he decided to fire my stoneware directly to 1,280 Celsius with a slow heating curve.  On the clay it was indicated to be fired at 1,150 - 1,280 Celsius. At that point I didn't knew what I know today. :)

Yesterday I applied high-fire glaze which is indicated to be fired at 1,200 - 1,240 Celsius on these 2 items and the glaze stayed in place very well. I don't understand how this happened as everybody is telling me that my clay has been vitrified and will not accept the glaze. The kiln owner confirmed again today that he bisque fired my items at 1,280 Celsius. 

Today the kiln owner fired my glazed 2 items to 1,200 Celsius, hopefully tomorrow he will get back to the shop and call me to come pick them up. Let's see tomorrow or on Saturday how it went.

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Perhaps in future you can try glazing directly on to the totally unfired pots.....raw glazing I know this as.  This cuts out the bisque firing but till needs the slow low temp rise of a bisque and your glazed need to tolerate being placed on unfired glaze.

Economically worth looking into. Lots of info in these forums. Search raw glazing and one time firing may be.

Old Lady here is a dab hand at this. Maybe pm her

Edited by Babs
errors

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To get a fully glazed foot, (going back to the original question), you can stand the body of the pot on "things" that raise it above the shelf.  Shelf posts, small pieces of broken kiln shelf.  So long as the pot is well supported, not just in the middle, it might not slump, and then you can have fully glazed feet.

I've done this several times, but beware that the pot can slump if not properly supported, and if the glaze runs it will drip straight onto the shelf, so catchers under the foot are useful.

This is not one of my pots, but something I'd love to create some time.

large.997402108_DrippyCakePlate.jpg.2a6f

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On a pot like the one in your picture, I think I would just leave the entire foot un-glazed.  There's a fairly distinct line where the pot ends and the foot begins, so should be pretty easy to get a clean edge, and have the glaze stop at along the same line.

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