|Monthly Tech-Tip |
A 325 screen has 325 wires-per-inch (the finer of the two screen closeups shown here). Those are grains of salt on it (45 micron openings, a typical human hair is 50-100 microns thick). A 40 mesh screen is much coarser, it has 425 micron openings (that is a particle of quartz trapped in an opening). A minus 45 mesh powder will be too fluffy to drop through a 325 screen. But particles smaller than 45 microns in a slurry will pass. To get a slurry through a screen this fine one needs to take special measures. It needs to have a high water content so it is fluid. Using a soft brush definitely helps. And a source of vibration. And it is necessary to clean the screen often to remove trapped oversize material. 325 mesh screen fabric is fragile and a sieve like this needs to be treated with care. Laboratory quality sieves cost hundreds of dollars (but can often be found used on ebay).
Sieves are important in ceramics for removing particulates and agglomerates from glaze, engobe and body slurries.
325 mesh (a sieve with 325 wires/inch) is the finest particle size that most ceramic minerals can be practically processed to (premium grades).
200 mesh (a sieve with 200 wires/inch) is the particle size that most minerals used in the ceramic industry are processed to.