I would add to Ron's comment that not all ancient porcelain was fired very hot. According to Nigel Wood there seems to be good evidence that some were fired in the region of 2250F, but held there for many many hours if not days. (No doubt it is probably still "Cone 10", but due to heatWORK not simply heat).

I'd also note that the Chinese themselves do not all accept the West's definition of porcelain - particularly in terms of translucency or vitrification. Many of the clay bodies (particularly the Northern Song bodies) would refer to what we call a white porcelaneous stoneware. (e.g. B-mix).
(I did a quick Google search and came up with these images for example):


On Mon, 12 Jul 2021 at 11:56, <ronroy@ca.inter.net> wrote:
What Mel is saying here may lead some potters to think it is 
impossible to make a cone 6 white clay body that does not leak.

I can do that, been doing it for 40 years. It's not impossible but you 
need to know what you are doing and keep an eye on any changes in the 
raw material.


Quoting mel jacobson <melpots@mail.com>:

> there is a very old saying.. porcelain is a white body, but, not all 
> white clay bodies are porcelain.
> one day we will go to a big show and the potter will be showing cone 
> 013 raku "ta dah" Porcelain...To even suggest
> the word "Porcelain" would mean to me that the work is cone 10-12.   
> It is totally vitrified, and will hold
> acid.   So much of what the vendors sell is "fluxed up" white clay 
> bodies and lets face it, no one really
> cares if it is "almost vitrified"  I know, semantics
> That is why the clay I started using is brown, and totally 
> vitrified. you control the color, the redart
> is the flux and makes it more workable.  I swear that in 2095 
> potters will be complaining their
> cone 6 "porcelain leaks". hell, it is not even very close to "white 
> stoneware".
> I sat a tall tumbler out of mel 6 clay on Mike Meyers (MN Clay 
> owner) desk and filled it with water.
> I said "keep it full for a month." he did.  not a drop of water on his desk.
>  I boiled  bars of  clay for  3 hours
> weighed them with a digital  scale.
>   perfect.
>   MEL
> website: www.melpots.com
> www.melpots.com/CLAYART.HTML

Ron Roy
Web page ronroy.net