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  

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!

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)

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

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

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

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.

... 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.