Bone china glazing problems

[Ben10]

Hey first post in this forum 

 

I try to use bone china since a month. They say everywhere, that I should high fire first. But of course if I do this the glaze does not stick afterwards. Is there any trick? Why should it be high fired first in general?

Sadly, I do not find a lot of information about bone china. So far I only found one page websites. Does someone has a good website about bone china?

 

Greetings from Estonia

 

[PeterH]

 

6 hours ago, Ben10 said:

I try to use bone china since a month. They say everywhere, that I should high fire first. But of course if I do this the glaze does not stick afterwards. Is there any trick? Why should it be high fired first in general?

... while waiting for the experts to arrive.

Sasha Wardell is an artist who works in bone china, her site is at  https://sashawardell.com/

Her 1st book Slipcasting contains some  bone china specific information.  I haven't seen her 2nd book Porcelain and Bone China but I expect it's well worth reading.

She gives an overview of porcelain vs bone china in Tempting Transparency https://tinyurl.com/mryx92z7

You need to high fire first because bone china has a short firing range and tends to warp. It's usual to use setters the support the work during this firing.
Obviously you cannot glaze the parts the setter touches, so glaze fire afterwards.

 

Glazing the vitrified body is difficult.  Heating the pots helps, as does spraying.

Tempting Transparency https://tinyurl.com/mryx92z7
Bone china has a low-glaze cycle following low-fire clay temperature ranges. The pieces need to be warmed up, usually to about 212°F (100°C) prior to glazing. This helps to evaporate water from the glaze slurry as it’s applied to the piece. When glazing, I pour glazes on the insides of the ware to line them and if I glaze the outsides, I spray them. Use a thicker application of glaze with a drop or two of gum Arabic added to the glaze to help with adhesion, as the body will have vitrified during the high firing.

Bone China https://digitalfire.com/glossary/bone+china
The process is completely different than what a potter would do: Bisque fire, glaze, high fire. Bone china is bisque fired to high fire and then glazed at a very low temperature. Since the porcelain has zero porosity, getting a glaze to stick and dry on it is not easy, the process needed goes well beyond what a normal potter would be willing to do.

PS If you are not using setters, then I don't see why you cannot do a normal-ish bisque firing. 

Edited March 27, 2022 by PeterH
added ps

[Ben10]

Thank you for the quite detailed info Peter!!

Warming them up I tried already, but only with a hairdryer. Spray painting I did not try so far. Making the glaze thicker is also a good hint.

Yes I dont use setters, I heard that ceramics with glaze on tend to deform more then without also. Still I will probably try and continue with the normal way. For my current project it is also not very important that it does not deform.

It is weird that it is written everywhere like a rule, that you have to fire higher first.

[Min]

Brushing glazes  with gums/binders are easier to apply to vitrified ware than dipping glazes, far more time consuming than spraying or dipping though.

Are you looking for the translucency of bone china?

[PeterH]

20 minutes ago, Ben10 said:

It is weird that it is written everywhere like a rule, that you have to fire higher first.

I can think of two possible reasons

1) Historically that's the way bone china was [always?] produced commercially.

2) You may only get marginal transparency gains from using bone china unless you make thin and fire close to warping. When you do - you need setters and hence a high bisque. If you don't - porcelain and white-stoneware are easier to use.

[Ben10]

Yes brushing with more thick glaze on a heated up porcelain might be an idea. I will try it all, because I have a lot of high fired bisque bone china already.

No I am looking for the snow white color on thin detailed porcelain. In my workshop I can fire at a maximum around 1260, so hard porcelain is not possible. I am not a big fan of slightly brownish porcelain. I heard there is new bone china where they use something else then bone ash which I would prefer, to not use animal bones. But I did not find a recipe yet.

 

Yes probably thats it, they go for the transparent. Bone china is deforming more in general, also glaze increases deforming. So they first fire high with setters. 

 

[PeterH]

24 minutes ago, Ben10 said:

I heard there is new bone china where they use something else then bone ash which I would prefer, to not use animal bones. But I did not find a recipe yet.

I think the recipe is essentially the same, substituting calcium triphosphate for bone ash.

Bone china https://digitalfire.com/glossary/bone+china
True bone china is a special type of translucent porcelain. Instead of feldspar as a flux, bone ash is used (today available in synthetic form tri-calcium phosphate).
... my note tricalcium phosphate is Ca3(PO4)2

Unfortunately the terminological plot thickens:

Phosphate Triphosphate https://en.wikipedia.org/wiki/Tricalcium_phosphate
Most commercial samples of "tricalcium phosphate" are in fact hydroxyapatite

Bone Ash https://digitalfire.com/material/123
Bone ash is TriCalcium Phosphate in the form of Hydroxyapatite Ca5(OH)(PO₄)3. This reacts when making bone china to give Anorthite (CaAl₂Si₂O₈) and Ca3(PO₄)2.
2*Ca5(OH)(PO₄)3 --> 3*Ca3(PO₄)2 + Ca(OH)2

So I've no idea if you you substitute 1:1 hydroxyapatite (sold as calcium triphosphate, or maybe synthetic bone ash) for "real bone ash". But it probably isn't far off.

[Min]

6 hours ago, Ben10 said:

I can fire at a maximum around 1260, so hard porcelain is not possible

Do you have access to halloysite? Image below from a Cone 6 (approx 1220C) halloysite claybody from a Canadian Supplier, mug made by Tony Hansen.  Grolleg makes a nice white porcelain too.

Edited March 28, 2022 by Min

[Ben10]

On 3/27/2022 at 11:04 PM, PeterH said:

I think the recipe is essentially the same, substituting calcium triphosphate for bone ash.

 

Cool thanks!! Sounds interesting. I will see if I will find something like this and where I can buy it!! I am really happy about the Info, lets see if I will manage.

Did not really understand the difference between Triphosphate and Hydroxyapatite, but hopefully I will find out, when I search for it.

 

On 3/28/2022 at 2:09 AM, Min said:

Do you have access to halloysite?

 

Never heard of it. It is new to me that the clay is that transparent and white. The supplies in Estonia can be quite limiting sometimes. But will stick with bone, since a little brownish accent is already annoying me and it will take some time to change everything.

 

So the first nonfunctional tests with normal firing cycle came out really good!! A beautiful white color, looks like hard porcelain  It seems extremely durable, like a stone. So the next step is to make it vegetarian.

[PeterH]

6 hours ago, Ben10 said:

Did not really understand the difference between Triphosphate and Hydroxyapatite, but hopefully I will find out, when I search for it.

My understanding was that everything for sale is probably mined as hydroxyapatite, but sold as either triphosphate or synthetic bone ash.

Two recipes:

[Ben10]

Thanks using similar recipe for casting slip:

Kaolin 30%

Bone Ash 45%

Feldspar 22,8%

Quarts 2,2%

Dispex 0,3%

 

Also tried with bentonite instead of dispex but it did not get it loose of the plaster.

It is interesting, that she says, that she prefers the chemical consistency of synthetic bone ash. The one who gave me recipe told me, some time it was better with bentonite and now with dispex, because the bone ash changed.

Will keep you updated!

[Min]

6 hours ago, Ben10 said:

Also tried with bentonite instead of dispex but it did not get it loose of the plaster.

 

6 hours ago, Ben10 said:

The one who gave me recipe told me, some time it was better with bentonite and now with dispex, because the bone ash changed.

Dispex is added to casting slips in very precise amounts to greatly reduce the amount of water needed in the slip while maintaining an optimum rheology.  Bentonite is sometimes added to casting slips to speed up the time it takes for the slip to release from the plaster mold.

Do you have a good source for tricalcium phosphate? It's very expensive where I live.

On 3/29/2022 at 2:44 AM, Ben10 said:

Never heard of it. It is new to me that the clay is that transparent and white.

Halloysite is a kaolin, the clay in the image I posted above uses a halloysite from New Zealand although there are deposits in other parts of the world. 

[Ben10]

On 3/31/2022 at 7:16 PM, Min said:

Do you have a good source for tricalcium phosphate? It's very expensive where I live.

No unfortunately so far I found nothing really, only in China, Australia or America.  I googled and asked around. I am looking for a supplier in Europa, because they might deliver it fast.  It seemes rather cheap in the most offers like 1.50€ for one kilo, but 60€ to ship :/.

 

Here are some examples

https://www.alibaba.com/product-detail/Manufacturer-sell-low-price-calcined-bone_62027820120.html?spm=a2700.galleryofferlist.normal_offer.d_title.20aad539KyHOjp

https://shop.walkerceramics.com.au/BA160.500/Bone-Ash-_dash_-Synthetic/pd.php

https://www.baileypottery.com/c-030-004.html

https://highwaterclays.com/products/synthetic-bone-ash

[PeterH]

16 minutes ago, Ben10 said:

No unfortunately so far I found nothing really, only in China, Australia or America.  I googled and asked around. I am looking for a supplier in Europa, because they might deliver it fast.  It seemes rather cheap in the most offers like 1.50€ for one kilo, but 60€ to ship :/.

 

Scarva offer it at a higher price, but lower postage. No claim this is best UKish  price available. https://tinyurl.com/2t33eypa

Partially completed order for 1kg

[Mark C.]

 I use this in my  synthetic iron glaze (Do you have a good source for tricalcium phosphate? It's very expensive where I live.)

I buy it in 50# bags and the price is always very high

Great stuff in a glaze subsitute for bone ash-my guess it better on the plaster surfaces as well.

[PeterH]

Naming an issue, see https://en.wikipedia.org/wiki/Calcium_phosphate
Tricalcium phosphate (tribasic calcium phosphate or tricalcic phosphate, sometimes referred to as calcium phosphate or calcium orthophosphate, whitlockite), E341(iii) (CAS#7758-87-4): Ca3(PO4)2

https://tinyurl.com/bdds5ssf

 

 

 

Edited April 2, 2022 by PeterH
tidied images

[Min]

With such a large amount of tricalcium phosphate needed to make bone china this is going to be an expensive way to get a white translucent body.  It's my understanding that originally bone china was made by using by bones from cattle slaughterhouses. The bones were available inexpensively (or free) so they were fired to create ash that was used in the claybody. It was a question of using what was available for little to no cost and on hand.

It would be easier, and in all probability far less expensive,  to make and fire a translucent white slip casting or plastic body at cone 6 (approx 1200C)  midrange body. You could fire to a typical bisque temperature of around cone 04 then glaze by dipping and fire to maturity. As the example of the yellow cup above with a good white kaolin like halloysite or grolleg you can get a very white body at midrange. 

[Ben10]

Thank you so much for the link! Was hesitating buying it, because I dont have the money lately, but now it is sold out. So maybe it should not happen. 

On 4/1/2022 at 11:55 PM, PeterH said:

 

 

For the Ebay offer, I am not really sure if it is the right one. It should be Ca3 (PO4)2 but it shows Ca5(OH)(PO4)3 when I google calcium phosphate tribasic. 

 

On 4/2/2022 at 7:52 PM, Min said:

It would be easier, and in all probability far less expensive,  to make and fire a translucent white slip casting or plastic body at cone 6 (approx 1200C)  midrange body. You could fire to a typical bisque temperature of around cone 04 then glaze by dipping and fire to maturity. As the example of the yellow cup above with a good white kaolin like halloysite or grolleg you can get a very white body at midrange. 

Yes, for now it is to much work, starting with a new material, finding recipes and I even would not know if I would be happy with the result.

The synthetic bone ash I would buy more as an experiment, but for long term I would have to find a cheaper supplier. 

[Denice]

Years ago I made several nativity sets out of bone slip that I purchased.   I made the molds myself and had a lot of joints which made  many seams on the pieces.   I bisque fired them and clean up the seams with a Dremel tool,  then I fired them to C5 using setters where they were needed.    I heated them in the oven before I glazed,  I know three firings is excessive but the process of cleaning the seams was very easy.   I used a Celadon type  low fire glaze and you couldn't find a joining seam on the pieces.    Denice

[Hyn Patty]

Back to the original question about how to get glazes to stick to bone china ... I glaze bone china all of the time.  Bisque fired first.  I airbrush my underglazes or glazes.  Once you get one layer on, you can fire it and then it's easy to brush on additional layers if you don't want to keep spraying.  Or use gum arabic to help apply brushing on the first layer.  Heating the bisque slightly can also help.  I see some of this was already mentioned above.  Also if silica is added to bone china (or frits, making it into lower firing fine bone china) then it's also easier to get glazes to adhere.  I'm fairly new to learning to mix my own slip so I'm still in a testing phase with that as most of my bisqueware has been imported from the UK in the past.

Good luck with it and I'll keep checking back to this thread, still learning as I go with casting my own bone china sculptures.  Here's a sample of some  equine pieces I've glazed - most (but not all) of these are fine bone china:  https://www.hynpatty.com/collections/163241

[williib]

Hi...FYI.

    the first time I used bone china.....luckily a few test beakers in a mini test kiln...I fired the traditional way.

ie. a bisque fire at 1000C.....polished the outside and then glazed the inside .....and fired to a higher temp. 1260-1280C

I found that the clay body and the glaze merged...not a pleasant result IMO.

Thats when i did some research and found that it needed to vitrify before glazing.

 

[Ben10]

Hi williib thank you for sharing  though probably because of a lack of my English skills I did not really understand, what you mean. Can you explain it more?

 

I am working with bone china again. I heard that people probably use special glazes for bone china which usually contain bone ash. Does anyone has experience with that? Is it necessary?

[Min]

16 hours ago, Ben10 said:

I heard that people probably use special glazes for bone china which usually contain bone ash. Does anyone has experience with that? Is it necessary?

It isn't necessary to include bone ash in the glaze recipe.

I believe @Hyn Patty uses bone china for some of her horses, try sending her a pm. (click on her name then the little envelope at the top of the screen and follow the prompts)

[Hyn Patty]

Any luck so far?  Yes, feel free to ping me and we can discuss it.   And no, you don't need any special glazes.  I glaze fine bone china all of the time using standard low fire glazes.  

Now the thread is about a year old I imagine you've moved on but if you are still having trouble getting your glaze to stick, you can also put a thin layer of white underglaze onto the china body first as that is often easier to get to stay put.  I use an airbrush but you can brush or sponge it thinly.  LOW fire it to something like cone 04. 

That'll give you a toothier surface to work with that can grab your real glaze layer you want over the surface.  Then fire normally at whatever cone you need for that last glaze layer - the underglaze will be fine.   DO NOT try to apply your glaze over the underglaze before you have fired the underglaze into place. Obviously if the other tricks mentioned earlier work, and can save you a step and a firing, that is better but this will also work if nothing else is!

When you overfire low fire overglazes they just turn glossy and go darker but if you use a white underglaze that won't matter.   It may knock down some of your transparency slightly, but assuming you apply it thinly in a single layer you probably won't even notice because it goes from opaque to pretty transparent once a glaze is applied over it.  Unless you put it on too thickly.

Another option of course (depending on the effects you are aiming for) is to skip a glaze entirely and use a low fire overglaze directly on your bisque.  China paints or enamels.  They don't handle like a glaze at all but still give you amazing effects.  Final finish can be adjusted with a flux layer over it for high gloss, satin, matte, etc.  The only limiting factor of using overglazes is that many of them can be toxic and not food safe.  There are however non-toxic varieties if you look around.  Good luck!

Edited February 26, 2023 by Hyn Patty

[Ben10]

Hey HynPatty, thank you for the tips, will keep them in mind!

Some bone china came out of the kiln this week, it seemed good, but the glaze dropped to the bottom of the cup and then it broke, because it could not shrink in the kiln.

I am only doing bone china time to time, but since a year. Sometimes it worked out fine, when I did a normal first fire and then a normal second fire with transparent glaze.

There are also some questions about the ingredients like which Kaolin (I think there are a few different options), but I will make a research later, since I probably won't have a studio to work in the next 6 month.

 

Your website is btw really impressive  

Edited February 26, 2023 by Ben10