Digitalfire Ceramic Glossary

This page has been deprecated

Please click the Glossary heading above for the new section.

• Ultimate Particles

  Physical particles of materials are those we can measure using ordinary sieves. Using water washing and standard wire mesh sieves it is normally only possible to determine the range of particle sizes of a powder sample down to 325 mesh (about 40 microns). However the particles measured by this means are agglomerates of hundreds or even thousands of ultimate particles. In ceramics, we are dealing with ultimate particles smaller than this in almost all materials. Ball clays, for example, have particles one tenth of a micron in size, 400 times smaller than 325 mesh. It is common for +95% of many materials to pass a 325 screen. Understanding materials fully means being aware of these particles, their sizes, shapes, densities, etc. An interesting example to illustrate is a water-washed and processed large-particle-size kaolin intended for the casting process. It is likely that 99.9% of such a material will wash right through a 325 mesh screen, making it appear to be a very fine powder. However the opposite is the case, in terms of ultimate particles and in relation to other clays, it has a very large particle size. On the other hand, a plastic kaolin may leave residue on a 200 mesh screen and appear to be coarser, whereas actually its ultimate particles could be 10 times smaller.
  
  To effectively measure ultimate particle sizes advanced testing equipment is needed. These devices use xray or photographic techniques. For example, many devices simply take a micro photograph of an air suspended powder sample and then software analyzes the photo to produce the desired measurement. The rate of sedimentation also reveals information about ultimate particles.

  Out Bound Links
  

  • (Glossary) Colloid

    Colloidal particles are so small and light that th...

  In Bound Links
  

  • (Glossary) Particle orientation

    Clay particles are flat and are either randomly or...

  • (Tests) AVPS - Average Particle Size (Microns)
  • (Tests) MDPS - Median Particle Size (Microns)
  • (Tests) L1M - % < 1 micron
  • (Tests) L2M - % < 2 microns
  • (Tests) L10M - % < 10 microns
  • (Tests) L20M - % < 20 microns
  • (Tests) UPSD - Ultimate Particle Size Distribution
  • (Tests) L5M - % < 0.5 microns
  • (Glossary) Clay Shrinkage

    All clays shrink during drying. Generally the amou...

  • (Glossary) Plasticity

    This term is used in reference to clays (or more o...

  
  Pictures
  This 1000 ml 24 hour sedimentation test compares Plainsman A2 ball clay ground to 10 mesh (left) with one that same material ball milled (right). There is no sediment in the milled material.
  
  
  Example of sedimentation test to compare soluble salts water extracts from suspended clay. This simple test also reveals ultimate particle size distribution differences in clays.
  
  
  

• Underglaze

  Oxide color mixtures which are applied to bisque or green ware and over which a transparent glaze is applied. To prevent excessive feathering of edges, underglazes are usually a mix of metallic oxides and a fritted stable glaze.

• Unity Formula

  A unity formula is just a formula that has been retotalled so that the RO group of oxides total one. This is also called a Seger formula and this standard provides the basis for comparing glazes. The three column format of expressing a formula was first used by Hermann Seger. The unity is normally set to the fluxes. Here is how we would recalculate the above raw formula to a flux unity formula:
  

             Raw              Unity
  
  Oxides     Formula          Formula
  
  -----------------------------------
  
  K2O         0.6  /  2.20  =  0.27
  
  CaO         1.3  /  2.20  =  0.59
  
  MgO         0.2  /  2.20  =  0.09
  
  ZnO         0.1  /  2.20  =  0.05
  
              -----           ----
  
  Flux Total  2.2              1.0
  
  Al2O3       0.9  /  2.20  =  0.41
  
  SiO2        9.0  /  2.20  =  4.09
  
  -----------------------------------

  Out Bound Links
  

  • (Library) Feldspar Teaches Us About Formulas, LOI, Unity

    The first chapter in the lessons section of the IN...

  In Bound Links
  

  • (Glossary) Mole%

    The Mole Percent (Mole%) calculation type has beco...

  • (Glossary) Analysis

    An analysis (or percentage analysis) is typically ...

  • (Glossary) LOI

    Simplistically, LOI is the amount of weight a mate...