How to determine whether ceramic pigments have lost their effectiveness

To determine whether a ceramic pigment has lost its effectiveness, one should not rely solely on its appearance; instead, a comprehensive assessment must consider both the powder’s physical state and the results of test firings. First, examine the powder: a properly functioning pigment will be loose and uniformly distributed. If large hard agglomerates are present that cannot be dispersed even after thorough kneading, it is highly likely that moisture absorption has caused clumping, leading to poor dispersion. Additionally, if foreign color powders or impurities are mixed in, resulting in discolored spots, this indicates cross-contamination and renders the pigment unsuitable for use. Appearance serves only as an initial screening tool; the critical step is conducting small‑scale test firings. Under consistent conditions—such as the same body and glaze, firing temperature, and atmosphere—compare the sample against the original standard. If the color deviates noticeably, appears dull or gray, or exhibits reduced tinting strength, or if defects like pinholes, glaze shrinkage, or pitting appear on the glaze surface, these signs indicate a change in the pigment’s performance. Furthermore, testing parallel samples from the same batch and observing diminished color reproducibility also points to an abnormality. Next, assess storage conditions: prolonged exposure to humid environments or damage to the packaging allowing dust ingress significantly increases the risk of degradation. Some pigments may retain their crystalline structure after absorbing moisture, yet suffer compromised dispersibility; in such cases, after thorough grinding and subsequent test firing, if color development recovers, the pigment can be evaluated for possible downgrading and continued use. Simply storing a pigment for an extended period does not necessarily mean it has failed; inorganic pigments kept sealed and dry maintain stable crystal structures. Ultimately, the test‑firing results should be taken as the definitive criterion. If agglomeration is severe and the pigment still yields abnormal results after grinding and re‑firing, it is advisable to discard it outright to prevent color‑variation defects in mass production.