FreeShip- Cornwall Stone, Substitute- (Prompt rebate on orders with 3 or more FreeShip items!)

CLICK THE "LEARN MORE ABOUT THIS ITEM" LINK JUST BELOW TO READ THE FULL DESCRIPTION FOR THIS ITEM.
*************************************************************
PROMPT REBATE ON ORDERS WITH 3 OR MORE “FreeShip” ITEMS! WANT TO KNOW YOUR TOTAL REBATE BEFORE PURCHASE? CONTACT US!
----> Go here to see listings for feldspar: <----
https://www.etsy.com/shop/NorthernWestStuff?ref=hdr_shop_menu&search_query=feldspar

Cornwall stone is one of the many ceramic materials that are no longer "original". The source mine is a mine that has "dried up". There is no longer true cornwall stone being sold. Ceramists knew the mineral composition, or "formula", and from that formula were able to construct a substitute. This particular substitute is quite close to the original. From here on, this description will call the material "CSS", "Cornwall Stone Substitute". CSS is a complex mix of minerals (which makes it and the original cornwall stone prone to being variable in composition). It is similar to feldspar and it's often used where a feldspar would be used, especially in glazes. It acts as a flux in glazes and clay bodies above cone 6. Another material that is similarly close to feldspar is nepheline syenite. It too is a mix of several minerals and is also similar to feldspar. But there are differences between CSS and feldspars.
Having said that, many sources call CSS a "type" of feldspar.

Here is a article from the Digital Fire ceramics database on cornwall stone substitutes, which pretty much sums it up:
{ https://digitalfire.com/4sight/education/substituting_cornwall_stone_194.html }:
"Cornwall Stone is used worldwide in ceramics as a source of fluxing oxides in both bodies and glazes. As a glaze material, Cornwall stone is akin to feldspar. It is sourced from granite rock and is, therefore, a combination of a number of minerals. Actually, there are several varieties depending on the state of alteration. The blue and purple colored types (less altered) contain more fluxes, while the whiter varieties contain less K2O, Na2O and almost no fluorine. For people who have used it in glazes like I have, it is hard to know whether the multiple personalities of the material are a result of grade confusion in the distribution channel or actual variability in the product. However, for many of us, it is the high cost of the material (to have it shipped half way across the world) that makes it well worth while to duplicate, that is, replace with a chemically equivalent mix of cheaper, more consistent, and easier to obtain materials."
...And here's a short article also from Digital Fire which discusses cornwall stone from a viewpoint of the original cornwall stone:
{ https://digitalfire.com/4sight/material/cornwall_stone_240.html } :
"Cornwall stone is a low iron feldspar material used primarily as a flux in clay bodies and glazes. Is mined in the Cornwall area of the UK. It melts 1150-1300C. It has a more diversified selection of fluxes than other feldspars but also has one of the highest silica contents. By itself it does not melt as well as feldspars (melt flow begins around cone 11 oxidation). It is popular in engobes for its adhesive power during and after firing and in glazes for its low shrinkage and minimal contribution to defects.
Long time users often comment on the difference in color between different batches of materials they receive. The parent ore materials are much more complex than other feldspars, and tend to be a mix of varying types of igneous rock in different stages of decomposition. Earlier stages of the ore materials are bluer (from fluorine) and contain more fluxes than newer rocks where some of the alkalis and fluorine have been leached and washed away creating a softer material. Cornish stones tend to be classified into major types according to the amount of flux present. Although Cornish stone is quite variable in composition, its low iron makes it an attractive material. Understandably, documentation on this material has provided a wide range of chemistries over the years, so no one really knows what a truly representative analysis should look like (the one provided here is an average of many that we have collected).
Its diversity of oxides make it similar in composition to common stone, thus its name. It is common to see synthetic substitutes for this material since it is easy to blend other feldspars to approximate the analysis of Cornish stone. These substitutes have the advantage of having no fluorine (which is suspected in various glaze faults that do not appear when using the substitutes). Hammill & Gillespie makes one of these, H&G Cornwall Stone. It is described in an article in Ceramics Technical Nov 2011, the chemistry given there differs from the chemistry we show here. The logic for the chemistry we show can be found in an article on this site (link below)."

Here is information on feldspars in general, which CSS is so close to, again from Digital Fire:
{ https://digitalfire.com/4sight/mineral/ceramic_mineral_feldspar_118.html } :
"An indispensable material in the ceramic industry. Most ceramic bodies employ feldspar as a flux to vitrify them at a lower temperature (the feldspar creates a glaze that glues the more refractory particles together to form the fired matrix). Most medium and high temperature glazes employ it as a flux. Feldspars are naturally occurring crystalline rocks that will melt and cool to form a glass (nature cooled them slowly (devitrified) to for crystalline minerals. There are many kinds of feldspars, but in ceramics soda, potash and lime feldspars are the most common.
Porcelains can contain up to 50% feldspar, stoneware bodies around 15%. Feldspar sources K2O and Na2O to glazes, these can produce very brilliant results. However, the high KNaO produces a high thermal expansion which in turn produces crazing. Thus it is important to control the amount of feldspar and employ materials that source other low expansion oxides like CaO, MgO, Li2O, BaO, SrO, etc."

Wikipedia lists some other things feldspars are used for { https://en.wikipedia.org/wiki/Feldspar }:
"Feldspar is a common raw material used in glassmaking, ceramics, and to some extent as a filler and extender in paint, plastics, and rubber. In glassmaking, alumina from feldspar improves product hardness, durability, and resistance to chemical corrosion. In ceramics, the alkalis in feldspar (calcium oxide, potassium oxide, and sodium oxide) act as a flux, lowering the melting temperature of a mixture. Fluxes melt at an early stage in the firing process, forming a glassy matrix that bonds the other components of the system together. In the US, about 66% of feldspar is consumed in glassmaking, including glass containers and glass fiber. Ceramics (including electrical insulators, sanitary ware, pottery, tableware, and tile) and other uses, such as fillers, accounted for the remainder.
In earth sciences and archaeology, feldspars are used for K-Ar dating, argon-argon dating, and luminescence dating.
In October 2012, the Mars Curiosity rover analyzed a rock that turned out to have a high feldspar content."-

=======================================================================

Reviews

Reviews (3)

Average:

Mar 27, 2024

Great transaction, fast shipping, good communication.

Lorrie Wickman

Dec 1, 2022

Megan

Oct 19, 2022

The product is Excellent!!!! and on time! fast shipping is important :)

Maria Soledad