A ceramic body slip stands in the pit for two hours, sheds clear water on top and sets hard below; the cast body comes out uneven in thickness and cracks after drying. The workshop habit is to add more clay to the ball mill or raise the moisture content, but once the slip is thinner the body strength drops again. Whether a slip is stable comes down to the charge on the particle surface and the particle-size distribution: clay minerals carry a negative charge by nature and are held in suspension by electrostatic and steric forces, and if the water-reducing agent is chosen wrongly the surface potential is suppressed and the slip flocculates and settles. Raising the moisture content only dilutes — it does not cure flocculation.
Whether the Slip Sheds Clear Water or Thickens Throughout Tells the Causes Apart
After standing, a slip that sheds clear water on top and turns dense and hard below is flocculating and settling: the particles cluster into large lumps and drop, which is tied to the type and dosage of the water-reducing agent. A slip that thickens evenly throughout and loses flow without separating is mostly low in moisture or under-milled in fineness, with a poor particle-size distribution. A slip with scum and bubbles on the surface has taken in impurities during milling or the water-reducing agent has gone wrong. When the same formula fails as soon as a different batch of clay is used, the clay's mineral composition has most likely changed and its response to the water-reducing agent has changed with it.
Order of Handling: Fix the Fineness and Moisture First, Then Adjust the Dispersant
First check the milling fineness and the particle-size distribution; if the fineness is short the particles settle quickly, so set the milling time and the charge properly. Next confirm that the slip's moisture is within the process range — too thin and the body strength suffers, too thick and both conveying and casting are hard work. Then adjust the type and dosage of the dispersant; adding it in the ball mill gives a more even result than topping up in the slip pit. After adding, measure the fluidity and the standing stability together — watching fluidity alone easily mistakes an overdose for an improvement.
Selection Points: Read Water-Reducing Efficiency and Settlement Resistance Separately
For a dispersant, first look at its water-reducing efficiency on the local clay; the mineral composition of clay from different mines differs greatly and the same product can behave completely differently in two places. Next look at its settlement resistance — a slip with poor standing stability cannot hold the thickness of a cast part. Third, look at how it fits the body process: the ions and organic matter it carries must burn off cleanly during firing and not affect the density or the glaze.
Chemi Tech Solutions
For ceramic bodies, glazes and casting systems, Chemi Tech has inorganic dispersants and organic polymer dispersants that can be used in milling, slip-pit adjustment and glaze preparation.
Compared with the inorganic type, the organic polymer type gives a more pronounced steric stabilisation of clay particles and better settlement resistance, suiting slips stored for long periods; the inorganic type has the edge in water-reducing efficiency and cost, suiting slips that demand high fluidity and turn over quickly; glaze systems care more about compatibility with the suspending agent, to avoid glaze stratification and uneven glaze thickness.
When the clay's mineral composition and the milling fineness fall short, a dispersant alone cannot produce a stable slip; such problems have to be solved at the raw material and the process. The specific fit and dosage must be judged by the system conditions.
Give the technical team the clay source, the mineral composition, the milling fineness and the standing requirement, and we will match the type accordingly, running a small sample before going to production. The inorganic dispersant solution and the ceramic glaze defoamer can be looked at first.
Summary
When a slip settles as soon as it stands, the cause often lies in the clay minerals and the milling fineness; the dispersant only amplifies or restrains the effect of those conditions and cannot replace the raw material and the fineness themselves. Build the particle-size distribution solidly, keep the moisture within the process window, and only then pick the type of dispersant — that is how stability is assured. When choosing, read water-reducing efficiency and settlement resistance separately, and give more weight to settlement resistance for slips stored for long periods. Chemi Tech has both inorganic and organic polymer dispersants for ceramic bodies and glazes, matched to the slip's own character.