Flint or Quartz? (uk suppliers)

[Joe_L]

A UK supplier lists both Flint (calcined) and Quartz 300. Which is more appropriate for mid and high fire glazes and when would I use one rather than the other?

I've heard flint can have a bit more calcium so this can be taken account of in a glaze calculation program. Of course the answer is test test test but before doing lots of undirected experimentation or being led down the garden path I'd be interested in people's thoughts?

Joe

[neilestrick]

Here in the US, flint is just a name we use for Silica, which is quartz. All the same thing. In my glaze calc software, there is no calcium or impurities of any sort, just pure silica. You would need to check with the manufacturer as to what impurities are actually in there, if any. @glazenerd can probably give more details on that. I expect that Quartz 300 means it is 300 mesh, which would be good for glazes.

[Joe_L]

Yes I think it does mean 300mesh.

Their website says "US recipes may state quartz when  they mean flint." which doesn't really help me choose which one to use when they offer both. As always in ceramics, they may both be essentially silica but small differences in origin or particle size can make significant differences in results.

[glazenerd]

Joe:

silica is mined in the USA from vast deposits: pure. Flint forms veins or seams ( like coal) along side other minerals which usually contain forms of calcium. So flint will have varying low levels of calcium . 

[neilestrick]

I've never seen a change in my glazes from different brands of silica. A trace amount of calcium shouldn't make a difference in most glazes.

[Chilly]

I have recipes that say "flint or quartz".

It would be nice to know what differnece ther really is. 

Have you contacted the supplier and asked them?

[neilestrick]

3 minutes ago, Chilly said:

I have recipes that say "flint or quartz".

It would be nice to know what differnece ther really is. 

Have you contacted the supplier and asked them?

In the US, flint and quartz and silica all mean the same thing.

US silica, which supplies most ceramics shops, says their ground silica products are at least 99.5% pure. Since flint additions in most glazes rarely exceed 35%, that puts the possible amount of impurities (calcium, etc) down to 0.16%, which won't show in a glaze.

[Mark C.]

Fint/silica all the same as Neil says-only difference is the mesh -Often sold as 200 mesh or 325mesh

I always use 325 as the melt is better in my glazes.

[High Bridge Pottery]

Not sure which supplier you are using but when I tried flint it was always a bit gritty and left lumps of flint in the fired glaze. Unless there is a massive price difference I would go with quartz. Pretty sure the glaze went through an 80 or 120 mesh but I am not 100% now. Get a bag of both and test 

[Joe_L]

Thanks Joel, I think that's the sort of stuff what I wanted to know. Although both are silica it's useful to understand the practical implications of using the different forms available in the UK. 

I often use CTM but other UK suppliers also list both too.

 

[Joe_L]

CTM say:

"As silica has a melting point around 1720oC it requires the eutectic effect of what is melting around it for it to melt at ceramic glaze firing temperatures – which is why small grain size is important to enable the other materials to surround each grain to make more localised eutectic effect.

Different people like different materials – the flint, being a natural silica combined material, will melt at a quicker rate than straight quartz but is not as pure in colour. So we use the quartz 300 in our stain based glazes especially to achieve the brighter colours and as we are mixing with a fritted base glaze the quartz melts OK, we use quartz 600 in the underglazes, if we were using all materials and not fritted base glaze I would use flint to encourage easier melting."