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Can I line a teapot with Terra Sig?


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#1 Nelly

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Posted 31 March 2013 - 10:23 PM

Dear All,

This is my second question of the day. I am in a run of making terra cotta teapots. It is my focused project for the next few months.

I have just finished a couple and want to coat not only the outside but inside with terra sig??

Is this possible if I want to use it as a functional piece?? Will it absorb the water and make the tea taste funny or simply break down more readily?? I have used a terra sig recipe using the clay I use for throwing (drying, decanting and the addition of sodium silicate).

On trips to China, I have seen those lovely pots they make that are sooooo smooth with that special clay.

Thus, in an effort to create or experiment with this technique I have been using my red rubber rib and a stone, burnishing and apply terra sig before I fire. I have done this on non-functional sculptural pieces. It looks amazing. Like chocolate. So smooth.

But now I want to do it with my tea pots. Inside and out.

If I was to hazard a guess, I would say most of you would say, yes do the outside but no, put a liner glaze on the inside if I want it to be truly functional.

My rationale is that it is not the same clay I saw in China. The terra cotta we have is commercially produced and does not likely have the same properties as that I saw when away.

Any ideas??

Nelly

#2 AtomicAxe

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Posted 31 March 2013 - 11:04 PM

Unless your clay body becomes vitreous in the low fire conditions that terra sig stays glossy looking ... it's NEVER going to be 'truly functional' ... the glaze will help, but even with a glaze ... liquid will seep into the clay body if the glaze has extremely minimal crazing in ideal situations. Sorry, just the breaks.

As for inside .. no, liner glaze. even though the terra sig can resist liquid penetrating it ... hot liquids will be able to soak, embed and stain the surface easier than cool liquids. plus, if you were just using it for water, no problem ... but tea ... you will be tasting the flavor of previous teas from the oils in the leaves that stick to the clay .... not ideal.

Now, if the question is really 'how do I make this truly functional?' ... vitreous clay body temp. if you're using porcelain or stoneware clay .... that is cone 6 or cone 10 depending on the clay ... terra cotta, some fire to cone 6, some to 06 to be vitreous ... that is up to you.

personally over time I like the tea oils to build up inside my tea pots ... but not inside the clay body, it is all surface build up. But then again, I also have 8 teapots each dedicated to a type of tea I like to drink.

#3 Nelly

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Posted 31 March 2013 - 11:27 PM

Unless your clay body becomes vitreous in the low fire conditions that terra sig stays glossy looking ... it's NEVER going to be 'truly functional' ... the glaze will help, but even with a glaze ... liquid will seep into the clay body if the glaze has extremely minimal crazing in ideal situations. Sorry, just the breaks.

As for inside .. no, liner glaze. even though the terra sig can resist liquid penetrating it ... hot liquids will be able to soak, embed and stain the surface easier than cool liquids. plus, if you were just using it for water, no problem ... but tea ... you will be tasting the flavor of previous teas from the oils in the leaves that stick to the clay .... not ideal.

Now, if the question is really 'how do I make this truly functional?' ... vitreous clay body temp. if you're using porcelain or stoneware clay .... that is cone 6 or cone 10 depending on the clay ... terra cotta, some fire to cone 6, some to 06 to be vitreous ... that is up to you.

personally over time I like the tea oils to build up inside my tea pots ... but not inside the clay body, it is all surface build up. But then again, I also have 8 teapots each dedicated to a type of tea I like to drink.


Dear Mr. AtomicAxe,

Let me see if I understand what you wrote.

Terra cotta is not ideal for a teapot unless I want to continue to taste the oils from previous tea. This is similar to the ones in China that I saw. The said the more you drink from them the more they absorb the oil to the point where all you have to do after a zillion cups is pour water into the pot without the leaves.

The liner glaze you say is likely a no go as it will stain and be non-functional.

My supplier says his majolica clay body when fired to 04 is as vitreous as clay at cone 6. So, I am still at a loss??

My guess is that the pot will weep. It will break down more readily with the terra sig on the inside but if it does build up a type of patina of tea oil, I will be happy. That is exactly what I am going for.

I hope I interpreted your message correctly. Correct me if I am wrong.

Perhaps I should put the terra cotta teapot on hold for now and do some simple things using the terra sig and Arbuckle glazes. Terra sig for the foot ring and/or lower half of the pot and the Arbuckle for a more permanent glaze.

Thank you so very much for your response.

Nelly

#4 Iforgot

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Posted 31 March 2013 - 11:49 PM

I am super curious about this too, do you think that if i applies Terra Sigilatta to a teapot made from stoneware and fired to ^6, would this be functional?



Darrel


Derek VonDrehle

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#5 weeble

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Posted 01 April 2013 - 05:49 AM

As I recall, terra sigillata was rediscovered and used as a cheap way to line terracotta sewer pipes, making them somewhat more water proof. I have often used it at cone 5 on vitrified clay exteriors on daily use things like mugs, (I hate the white foot on a colored cup!) but I still like to use a regular glaze on the inside and lip as the terra sig can stain somewhat with use. I imagine you COULD use a teapot with terra sig, provided you used terra sig without added stain, (I'd be concerned the stain might leach) and if you were not concerned with gunk growing on the inside of your teapot. Even polished, the surface of the terra sig is like unglazed clay, rather rough and likely to provide lots of growing places for bio-films. On an interior, there is really no reliable way to polish the entire surface, so I think you'd be much more likely to run into issues with gunk. I wouldn't even THINK of selling a piece with terra sig inside for anything like a tea cup or pot.
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#6 TJR

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Posted 01 April 2013 - 08:19 AM


Unless your clay body becomes vitreous in the low fire conditions that terra sig stays glossy looking ... it's NEVER going to be 'truly functional' ... the glaze will help, but even with a glaze ... liquid will seep into the clay body if the glaze has extremely minimal crazing in ideal situations. Sorry, just the breaks.

As for inside .. no, liner glaze. even though the terra sig can resist liquid penetrating it ... hot liquids will be able to soak, embed and stain the surface easier than cool liquids. plus, if you were just using it for water, no problem ... but tea ... you will be tasting the flavor of previous teas from the oils in the leaves that stick to the clay .... not ideal.

Now, if the question is really 'how do I make this truly functional?' ... vitreous clay body temp. if you're using porcelain or stoneware clay .... that is cone 6 or cone 10 depending on the clay ... terra cotta, some fire to cone 6, some to 06 to be vitreous ... that is up to you.

personally over time I like the tea oils to build up inside my tea pots ... but not inside the clay body, it is all surface build up. But then again, I also have 8 teapots each dedicated to a type of tea I like to drink.


Dear Mr. AtomicAxe,

Let me see if I understand what you wrote.

Terra cotta is not ideal for a teapot unless I want to continue to taste the oils from previous tea. This is similar to the ones in China that I saw. The said the more you drink from them the more they absorb the oil to the point where all you have to do after a zillion cups is pour water into the pot without the leaves.

The liner glaze you say is likely a no go as it will stain and be non-functional.

My supplier says his majolica clay body when fired to 04 is as vitreous as clay at cone 6. So, I am still at a loss??

My guess is that the pot will weep. It will break down more readily with the terra sig on the inside but if it does build up a type of patina of tea oil, I will be happy. That is exactly what I am going for.

I hope I interpreted your message correctly. Correct me if I am wrong.

Perhaps I should put the terra cotta teapot on hold for now and do some simple things using the terra sig and Arbuckle glazes. Terra sig for the foot ring and/or lower half of the pot and the Arbuckle for a more permanent glaze.

Thank you so very much for your response.

Nelly

Nelly;
I think you got your answer from Atom Axe and the rest. I would put your Arbuckle white matt on the inside and terra sig the outside. I don't think the terra sig would hold uo on the inside without seepage. We use two teapots, one for black tea and one for green teas. We never wash either, just rinse them out. Both are Cone 10 stoneware, and are pretty stained on the inside. Maybe you could try one and see if it works before you sell any.
TJR.

#7 Nelly

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Posted 01 April 2013 - 09:51 AM

As I recall, terra sigillata was rediscovered and used as a cheap way to line terracotta sewer pipes, making them somewhat more water proof. I have often used it at cone 5 on vitrified clay exteriors on daily use things like mugs, (I hate the white foot on a colored cup!) but I still like to use a regular glaze on the inside and lip as the terra sig can stain somewhat with use. I imagine you COULD use a teapot with terra sig, provided you used terra sig without added stain, (I'd be concerned the stain might leach) and if you were not concerned with gunk growing on the inside of your teapot. Even polished, the surface of the terra sig is like unglazed clay, rather rough and likely to provide lots of growing places for bio-films. On an interior, there is really no reliable way to polish the entire surface, so I think you'd be much more likely to run into issues with gunk. I wouldn't even THINK of selling a piece with terra sig inside for anything like a tea cup or pot.


Dear Weeble,

Thank you so much for your response. Please know I am a hobby potter. I do not sell. I give a lot of my stuff away.

I do, however, appreciate your candor in your response. As I said, after rethinking it last night, I have decided to simply make my tea pots in stone ware. Those that are made, I will play with in terms of decoration.

Know that I generally use terra sig for foot rings and the lower half or third of a pot on the outside.

I do use it to crank up my sculptural ware and make it more touchable.

Know that the pieces that came out of the kiln that I was blown away by were bisque fired only. Perhaps this is why they retained their high polish.

Thank you so much for your response.

Nelly

#8 Nelly

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Posted 01 April 2013 - 09:59 AM



Unless your clay body becomes vitreous in the low fire conditions that terra sig stays glossy looking ... it's NEVER going to be 'truly functional' ... the glaze will help, but even with a glaze ... liquid will seep into the clay body if the glaze has extremely minimal crazing in ideal situations. Sorry, just the breaks.

As for inside .. no, liner glaze. even though the terra sig can resist liquid penetrating it ... hot liquids will be able to soak, embed and stain the surface easier than cool liquids. plus, if you were just using it for water, no problem ... but tea ... you will be tasting the flavor of previous teas from the oils in the leaves that stick to the clay .... not ideal.

Now, if the question is really 'how do I make this truly functional?' ... vitreous clay body temp. if you're using porcelain or stoneware clay .... that is cone 6 or cone 10 depending on the clay ... terra cotta, some fire to cone 6, some to 06 to be vitreous ... that is up to you.

personally over time I like the tea oils to build up inside my tea pots ... but not inside the clay body, it is all surface build up. But then again, I also have 8 teapots each dedicated to a type of tea I like to drink.


Dear Mr. AtomicAxe,

Let me see if I understand what you wrote.

Terra cotta is not ideal for a teapot unless I want to continue to taste the oils from previous tea. This is similar to the ones in China that I saw. The said the more you drink from them the more they absorb the oil to the point where all you have to do after a zillion cups is pour water into the pot without the leaves.

The liner glaze you say is likely a no go as it will stain and be non-functional.

My supplier says his majolica clay body when fired to 04 is as vitreous as clay at cone 6. So, I am still at a loss??

My guess is that the pot will weep. It will break down more readily with the terra sig on the inside but if it does build up a type of patina of tea oil, I will be happy. That is exactly what I am going for.

I hope I interpreted your message correctly. Correct me if I am wrong.

Perhaps I should put the terra cotta teapot on hold for now and do some simple things using the terra sig and Arbuckle glazes. Terra sig for the foot ring and/or lower half of the pot and the Arbuckle for a more permanent glaze.

Thank you so very much for your response.

Nelly

Nelly;
I think you got your answer from Atom Axe and the rest. I would put your Arbuckle white matt on the inside and terra sig the outside. I don't think the terra sig would hold uo on the inside without seepage. We use two teapots, one for black tea and one for green teas. We never wash either, just rinse them out. Both are Cone 10 stoneware, and are pretty stained on the inside. Maybe you could try one and see if it works before you sell any.
TJR.


Dear TRJ,

Again, thank you for your response.

That is what I will do. I read last night quite a bit about the unique clay that goes into those pots from China (Yixing) I think it is called. THAT was the look and finish I was hoping for but if the clay I am using doesn't permit this finish, I am fine with this. When in clay, you just adjust. That is life.

I think, as I said, I will stop making tea pots in terra cotta. There are lots of other options. I will try one though lined with the Arbuckle for fun.

Thank you so much for getting back to me.

Nelly

#9 AtomicAxe

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Posted 01 April 2013 - 10:37 AM


Unless your clay body becomes vitreous in the low fire conditions that terra sig stays glossy looking ... it's NEVER going to be 'truly functional' ... the glaze will help, but even with a glaze ... liquid will seep into the clay body if the glaze has extremely minimal crazing in ideal situations. Sorry, just the breaks.

As for inside .. no, liner glaze. even though the terra sig can resist liquid penetrating it ... hot liquids will be able to soak, embed and stain the surface easier than cool liquids. plus, if you were just using it for water, no problem ... but tea ... you will be tasting the flavor of previous teas from the oils in the leaves that stick to the clay .... not ideal.

Now, if the question is really 'how do I make this truly functional?' ... vitreous clay body temp. if you're using porcelain or stoneware clay .... that is cone 6 or cone 10 depending on the clay ... terra cotta, some fire to cone 6, some to 06 to be vitreous ... that is up to you.

personally over time I like the tea oils to build up inside my tea pots ... but not inside the clay body, it is all surface build up. But then again, I also have 8 teapots each dedicated to a type of tea I like to drink.


Dear Mr. AtomicAxe,

Let me see if I understand what you wrote.

Terra cotta is not ideal for a teapot unless I want to continue to taste the oils from previous tea. This is similar to the ones in China that I saw. The said the more you drink from them the more they absorb the oil to the point where all you have to do after a zillion cups is pour water into the pot without the leaves.

The liner glaze you say is likely a no go as it will stain and be non-functional.

My supplier says his majolica clay body when fired to 04 is as vitreous as clay at cone 6. So, I am still at a loss??

My guess is that the pot will weep. It will break down more readily with the terra sig on the inside but if it does build up a type of patina of tea oil, I will be happy. That is exactly what I am going for.

I hope I interpreted your message correctly. Correct me if I am wrong.

Perhaps I should put the terra cotta teapot on hold for now and do some simple things using the terra sig and Arbuckle glazes. Terra sig for the foot ring and/or lower half of the pot and the Arbuckle for a more permanent glaze.

Thank you so very much for your response.

Nelly


There is a difference in the thin layers of tea oils sticking to the inside of a teapot and water with the oil embedding in the clay body and spoiling ... imagine if you will you take a cup that you leave tea in the bottom till it gets old and nasty then dries out ... then pour a new cup of tea into it. Not ideal. that is what happens. ... glaze prevents this, but as I said, if your clay body itself is not vitreous ... it will still seep into the clay body.

You can fire terra sig to higher temps than cone 06 ... but the higher you go, the less glossy and smooth looking it is. On creative pieces, terra sig is more of a glazeless smooth and glossy surface that does not have the same finish as burnishing raw clay. The effect of terra sig and burnishing is close knit clay that is semi water resistant ... but not water proof like a thin layer of glass.

Also, you can use terra cotta clay for teapots, as well as all functional ware ... but again, as with all other clays, it needs to be vitreous at the temp you fire to. Using clay for functional products that is not vitreous sets yourself up for a bad reputation since people will not know the difference between the two ... and all it takes is a mug in a microwave that had enough time to seep water into the clay body to set about some rather bad popcorn effects in said microwave.

#10 Iforgot

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Posted 05 April 2013 - 10:46 PM



Unless your clay body becomes vitreous in the low fire conditions that terra sig stays glossy looking ... it's NEVER going to be 'truly functional' ... the glaze will help, but even with a glaze ... liquid will seep into the clay body if the glaze has extremely minimal crazing in ideal situations. Sorry, just the breaks.

As for inside .. no, liner glaze. even though the terra sig can resist liquid penetrating it ... hot liquids will be able to soak, embed and stain the surface easier than cool liquids. plus, if you were just using it for water, no problem ... but tea ... you will be tasting the flavor of previous teas from the oils in the leaves that stick to the clay .... not ideal.

Now, if the question is really 'how do I make this truly functional?' ... vitreous clay body temp. if you're using porcelain or stoneware clay .... that is cone 6 or cone 10 depending on the clay ... terra cotta, some fire to cone 6, some to 06 to be vitreous ... that is up to you.

personally over time I like the tea oils to build up inside my tea pots ... but not inside the clay body, it is all surface build up. But then again, I also have 8 teapots each dedicated to a type of tea I like to drink.


Dear Mr. AtomicAxe,

Let me see if I understand what you wrote.

Terra cotta is not ideal for a teapot unless I want to continue to taste the oils from previous tea. This is similar to the ones in China that I saw. The said the more you drink from them the more they absorb the oil to the point where all you have to do after a zillion cups is pour water into the pot without the leaves.

The liner glaze you say is likely a no go as it will stain and be non-functional.

My supplier says his majolica clay body when fired to 04 is as vitreous as clay at cone 6. So, I am still at a loss??

My guess is that the pot will weep. It will break down more readily with the terra sig on the inside but if it does build up a type of patina of tea oil, I will be happy. That is exactly what I am going for.

I hope I interpreted your message correctly. Correct me if I am wrong.

Perhaps I should put the terra cotta teapot on hold for now and do some simple things using the terra sig and Arbuckle glazes. Terra sig for the foot ring and/or lower half of the pot and the Arbuckle for a more permanent glaze.

Thank you so very much for your response.

Nelly


There is a difference in the thin layers of tea oils sticking to the inside of a teapot and water with the oil embedding in the clay body and spoiling ... imagine if you will you take a cup that you leave tea in the bottom till it gets old and nasty then dries out ... then pour a new cup of tea into it. Not ideal. that is what happens. ... glaze prevents this, but as I said, if your clay body itself is not vitreous ... it will still seep into the clay body.

You can fire terra sig to higher temps than cone 06 ... but the higher you go, the less glossy and smooth looking it is. On creative pieces, terra sig is more of a glazeless smooth and glossy surface that does not have the same finish as burnishing raw clay. The effect of terra sig and burnishing is close knit clay that is semi water resistant ... but not water proof like a thin layer of glass.

Also, you can use terra cotta clay for teapots, as well as all functional ware ... but again, as with all other clays, it needs to be vitreous at the temp you fire to. Using clay for functional products that is not vitreous sets yourself up for a bad reputation since people will not know the difference between the two ... and all it takes is a mug in a microwave that had enough time to seep water into the clay body to set about some rather bad popcorn effects in said microwave.



I would not recommend using terra cotta for the teapot because even though earthen ware clays are marketed as being vitreous at ^06-04 the surface remains very porous, which can harbor bacterial growth if not glazed. stick to stoneware.
Derek VonDrehle

Raku, Pit fired, Majolica, and Stoneware ceramic artisit

#11 Nelly

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Posted 06 April 2013 - 12:10 AM




Unless your clay body becomes vitreous in the low fire conditions that terra sig stays glossy looking ... it's NEVER going to be 'truly functional' ... the glaze will help, but even with a glaze ... liquid will seep into the clay body if the glaze has extremely minimal crazing in ideal situations. Sorry, just the breaks.

As for inside .. no, liner glaze. even though the terra sig can resist liquid penetrating it ... hot liquids will be able to soak, embed and stain the surface easier than cool liquids. plus, if you were just using it for water, no problem ... but tea ... you will be tasting the flavor of previous teas from the oils in the leaves that stick to the clay .... not ideal.

Now, if the question is really 'how do I make this truly functional?' ... vitreous clay body temp. if you're using porcelain or stoneware clay .... that is cone 6 or cone 10 depending on the clay ... terra cotta, some fire to cone 6, some to 06 to be vitreous ... that is up to you.

personally over time I like the tea oils to build up inside my tea pots ... but not inside the clay body, it is all surface build up. But then again, I also have 8 teapots each dedicated to a type of tea I like to drink.


Dear Mr. AtomicAxe,

Let me see if I understand what you wrote.

Terra cotta is not ideal for a teapot unless I want to continue to taste the oils from previous tea. This is similar to the ones in China that I saw. The said the more you drink from them the more they absorb the oil to the point where all you have to do after a zillion cups is pour water into the pot without the leaves.

The liner glaze you say is likely a no go as it will stain and be non-functional.

My supplier says his majolica clay body when fired to 04 is as vitreous as clay at cone 6. So, I am still at a loss??

My guess is that the pot will weep. It will break down more readily with the terra sig on the inside but if it does build up a type of patina of tea oil, I will be happy. That is exactly what I am going for.

I hope I interpreted your message correctly. Correct me if I am wrong.

Perhaps I should put the terra cotta teapot on hold for now and do some simple things using the terra sig and Arbuckle glazes. Terra sig for the foot ring and/or lower half of the pot and the Arbuckle for a more permanent glaze.

Thank you so very much for your response.

Nelly


There is a difference in the thin layers of tea oils sticking to the inside of a teapot and water with the oil embedding in the clay body and spoiling ... imagine if you will you take a cup that you leave tea in the bottom till it gets old and nasty then dries out ... then pour a new cup of tea into it. Not ideal. that is what happens. ... glaze prevents this, but as I said, if your clay body itself is not vitreous ... it will still seep into the clay body.

You can fire terra sig to higher temps than cone 06 ... but the higher you go, the less glossy and smooth looking it is. On creative pieces, terra sig is more of a glazeless smooth and glossy surface that does not have the same finish as burnishing raw clay. The effect of terra sig and burnishing is close knit clay that is semi water resistant ... but not water proof like a thin layer of glass.

Also, you can use terra cotta clay for teapots, as well as all functional ware ... but again, as with all other clays, it needs to be vitreous at the temp you fire to. Using clay for functional products that is not vitreous sets yourself up for a bad reputation since people will not know the difference between the two ... and all it takes is a mug in a microwave that had enough time to seep water into the clay body to set about some rather bad popcorn effects in said microwave.



I would not recommend using terra cotta for the teapot because even though earthen ware clays are marketed as being vitreous at ^06-04 the surface remains very porous, which can harbor bacterial growth if not glazed. stick to stoneware.



Yeah, in the end, I think you are right. I will stick to stone ware for my teapots. Too much trouble and too many things to think about. I will use the terra cotta for bowls and some sculptural pieces. Done. Thank you all for clearing up this question for me.

Nelly




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