In ceramic factories, a common situation arises: the same deflocculant works well in the backing (standard body), with slurry flowing smoothly; but when switched to the surface (decorative layer) formulation at the same dosage, the slurry becomes noticeably thicker and the flow rate drops significantly.

Most people's first reaction is "the deflocculant is no good" or "the wrong deflocculant was chosen." But the more fundamental reason is: a deflocculant is not a universal cure-all — its effectiveness is highly dependent on the characteristics of the "body formulation soil" itself. When the "soil" of the formulation changes, the "fertilizer" effect of the deflocculant naturally differs.

The core of ceramic body formulations is clay minerals, and different clay minerals have vastly different crystal structures, surface charge characteristics, and cation exchange capacities (CEC). The response of a deflocculant to different clay minerals is essentially a matching problem of "prescribing the right remedy."

For a deflocculant to work, it must first adsorb onto particle surfaces. The finer the particles, the larger the specific surface area, and the more deflocculant molecules are needed.

One of the core mechanisms of deflocculation is electrostatic repulsion — giving particle surfaces enough negative charge so they repel each other and disperse. But different body formulations have different surface charge characteristics, and the repulsion strength a deflocculant can establish also differs.

• Isoelectric Point (IEP) Differences: Kaolin's IEP is typically at pH 3–5; bentonite, due to permanent negative charge, has a lower IEP or even no obvious IEP. Different clay types in body formulations mean different IEPs, and the deflocculant must push pH "away from the isoelectric point" to be effective. Under the same pH conditions, one formulation may already be far from the IEP while another is still near it — deflocculation results differ dramatically.
• Edge Positive Charge Strength Differences: Kaolin edges carry strong positive charges, easily forming "face-to-edge" attraction (card house structure) with negative faces. The deflocculant must preferentially neutralize edge positive charges. Different formulations have different edge proportions, and deflocculant requirements also differ.
• Charge Density Differences: Montmorillonite has high face charge density but uniform distribution; kaolin has low charge density but strong edge activity. The deflocculant's adsorption capacity and repulsion effect on these two surfaces are completely different.

Many body formulations (especially ball clay, bentonite, and some kaolin) contain natural organic matter such as humic acid, lignin, and organic acids. To deflocculants, these organics are "invisible consumers."

This is why surface formulations with higher organic content often require higher deflocculant dosage, or even a deflocculant grade with stronger resistance to organic interference. If the backing body has low organic content, the same deflocculant naturally "achieves twice the result with half the effort."

Different body formulations vary greatly in soluble salt content and type. When these soluble salts enter the slurry, they change the system's ionic environment and directly interfere with the deflocculant's action.

In addition to clay, body formulations also contain lean materials such as quartz and feldspar. Different ratios and particle sizes of lean materials affect particle packing density and slurry rheological behavior.

• High lean material ratio (common in backing bodies): Quartz and feldspar particles are coarser, with small specific surface area, and do not consume deflocculant; meanwhile, the "skeleton" formed by coarse particles favors slurry flow. The deflocculant mainly acts on a small amount of clay, with concentrated and obvious effects.
• Low lean material ratio (common in surface formulations): High proportion of fine particles, high packing density, small inter-particle voids, and little free water; the deflocculant must simultaneously handle surface coverage of more fine particles and release of void water — increasing difficulty.
• Unreasonable particle gradation: If coarse and fine particles are poorly matched (e.g., too much or too little fine powder), the slurry's packing density and fluidity are inherently suboptimal — even the strongest deflocculant cannot "turn the tide."

Combining all the factors above, we can clearly explain the common phenomenon of "backing disperses, surface doesn't":