Unknown Glaze? This is actually Greenstone ...

While I am packing boxes prior to moving, I found the condiment set above, and... it clearly reads on the side of the box,salt, pepper, sauce jug, mustard pot! So finally that one can be put to rest!   

Thanks Thelma, but now we will have to find another shape number for it.
I found a salt and pepper in this glaze recently

It's exhumation time!

This should also form part of the discussion on hotel stacking, but I will sort that later.

I have just been looking through Jonty Valentine's Mark Cleverley monograph. ("Mark Cleverley Designer" [Objectspace "Master of Craft" series], Jonty Valentine, Bateman, 2014)

Jonty has reproduced in its entirety an article from Designscape magazine in which Mark Cleverley was interviewed about the new hotel ware designs. (Designscape 58 May 1974, pp5-7 "Stacks of Crockery")

"The thinking was originally for two new cups, two new cream jugs, a sugar with lid and a pepper and salt.
"To this request was added the egg cup and teapot to be produced at a later date ..."

A photograph of the teapot is shown: I don't know if that ever made it to market.
In a photo of the various pieces the eggcup is just seen under one of the condiments. There is no mention of a mustard in the text.

I believe that the shape later marketed as a mustard pot is the same eggcup shape, and that a search for a mustard shape number, different from the eggcup shape number, would be futile.

I haven't sat down and read the whole book yet, but hope to have done so by the Exhibition opening.