What Is The Difference Between Silica 200 And Silica 325 Mesh?

[Pugaboo]

I am starting to set up a basic slip and glaze pantry. When recipes call for silica do they want 200 mesh or 325 mesh? What is the difference and if you were to have one and not the other which is best to have?

 

I ask because I have a slip recipe asking for silica AND a glaze recipe asking for silica but no number. The website I will order from has the 2 different mesh numbers. Do both recipes use the same mesh?

 

Terry

[Guest JBaymore]

Mesh size is basically particle size.  325 m is finer sized particles than 200 m. 

 

While if a reaction is allowed to go to completion in ceramic chemistry, and the glaze does what glass artists call "fine out" (all possible reactions go to completion)....... the particle size of flint would make no difference.  However, the WAY a glaze melts can affect how it looks sometimes.

 

As a general rule smaller particles of glaze materials start to become involved in the melt earlier than other larger particles (even of the same materials) given the same heatwork.  So technically 325 mesh flint will started to become involved with the surrounding chemistry (particles of fluxes, etc.) earlier than a glaze made with 200 m flint.

 

So the two side by side glazes... one with 200 and one with 325, for a given firing profile MIGHT looks a slight bit different.  But it likely will be subtle.  Generally speaking the faster the firing up rate profile the more likely you will see differences.

 

There could be other reasons to use a mixture of particle meshes in specialized cases.  The property in this case is called "packing".  It has to do with how the various materials "fit" together as the wet glaze layer sets up on the work.  It can affect how "tough" the dry (not fired) glaze layer is, and also the way that the melt starts to happen due to the intimacy of contact between particles (and lack of air spaces in the grains).  This stuff is usually the province of industry; most studio potters don't address this issue.

 

As a "standard", 325 mesh is used in glazes and slips, and 200 mesh is used in clay bodies.

 

Hope that helps.

 

best,

 

.....................john

[Pugaboo]

Thank you for explaining it. I will get the 325

 

T

[docweathers]

John

 

If I wanted to take advantage of the packing to make wet glaze tougher, what might be a good ratio of the two to start experimenting with?

 

Larry

[glazenerd]

 

JBaymore

and the glaze does what glass artists call "fine out" (all possible reactions go to completion)..

known in chemistry as "equilibrium."  Cone 6 needs 325 mesh, or additional fluxes for full melt of 200 mesh: which could cause other problems. Cone 10 has the extra heat to get a complete melt of 200 mesh with usual flux additions. 200 mesh is a clay body primarily.

Nerd