Cream of Tartar

So...........what does the name conjor up for you? For me it means the white powder that you buy in tubs from the bakery section of a Supermarket or Grocers store. I have no idea where the name "cream of tartar" comes from, but  historically, it was the "leys of wine" the powdery sediment found on the walls of wine cellar vats. Then it was given the name "Argol" and it could be red or white depending on the colour of the wine it came from!

 There appear to be many names for the chemical - the commonest I have found are Potassium Hydrogen Tartrate or Potassium Bitartrate, but you can also find monopotassium tartrate, potassium acid tartrate,

[R-(R*,R*)]-2,3 Dihydroxybutanedioic Acid Monopotassium Salt, Potassium (2R,3R)-3-carboxy-2,3-dihydroxypropanoate, and more.......!

The chemical formula can be written KC₄H₅O₆ 

or even

C4H4O4 (OH) (OK)

Its CAS  number is 868-14-4 (One of the commonest classifications to stop confusion between chemicals)

CB number -CB7854493

formula weight:188.18
E number - E-336(i)

  It is the mineral acid salt of Tartaric Acid and probably best known for its stabilizing properties when making meringues. It is a component in Baking Powder and also a chemical buffer.

So I can now see you wondering what this post is all about!

Many dye recipes both historical and modern recommend the use of Argol  or Cream of Tartar as an addition to alum in the mordanting process, it is there to assist the alum in mordanting wool with salts of Aluminium, Chromium, Iron, Copper and Tin. It is said to improve the permanence, fulness nad brilliance of the ultimate colour. For the chemists amongst you this is surmised to be due to the double decomposition of the tartrate and the mordanting salt, the mineral acid of the latter combining with the potassium of the tartrate and the metallic hydrate with tartaric acid, (it is also possible that a double salt is formed).

Given all the above information I am struggling to understand why several dye retailers in the UK make a claim that the Cream of Tartar sold for catering is a substitute chemical not suitable for use as the mordant assistant.

So what is this substitute? I cannot find it - is it the same product but using one of its other names?

For my own peace of mind I have comtacted Dr Oetker and Tesco both of whom are very clear that the product they sell under the name Cream of Tartar is CAS number 868-14-4 Potassium Hydrogen Tartrate (etc, etc) I have their replies in email format so if you wish to see them I am happy to forward on - or feel free to contact them yourself.

I feel so strongly that we should be able to buy the product we want under the name that it is known by that I would like to find out more on the subject of this "substitute" used for catering. Maybe if there is a substitute we should be considering approaching Trading Standards to get the name used as it should be and another name for the alternative!