Ceramicware Defects Handbook/Specking

Specking

Specking can caused by a great variety of sources, To narrow down the potential causes, it would be best to break up the wares to observe if the specking is observed inside the ceramic wares or merely on surface If observed inside and outside of the ceramic wares, it is highly caused during body preparation stages If observed at both top and bottom facing, it implies it occurs during the early stages of clay processing Brown or black specking may occurs due presence of iron contaminants Sources of the contaminants are as followed:

Presence of iron / rusts insisde the slip. Use double/triple sieve with decreasing aperture sizes (or deck sifters). Sieves should be magnetted to removed iron particles and magnets should be regularly cleaned.
Regulary checking on slip storage do not have contaminants
Filtered pressed cakes may be contaminated by pallets rusted nails
During rainy seasons, the rain drops may bring the rusts of rooftop trusses possible dripping on clay cakes
Electromagnet are not functioning
Pug mills rusted in the barrel screws (No proper maintainence)
Airborne dust that maybe blown around due to poorly design ventilations/ blower fans
Exhaust discharge from grinding wheels. Silicone carbide are notorious specking agent and if possible, use sintered alumina
Contaminations in water supply due to rusted metal
Particles that are logged in to the kiln shelf onto ware below. Placing the wares from topmost shelf slowly downard to bottom to minimses any of the dislodged particles fall to the shelf below
Contamination of the glazes (dipping) Keeping glaze tub covered when not in use.
Repair technician perform repairing which includes but not limited to metal cutting, welding metals, knocking metals by hammers/chisels which may cause debris of iron particles spreading especially if it is near or inside production area
Inadequate cleaning of kiln may causes kiln's batt particle to be spread over