Zinc yellow (K₂O^*4ZnCrO₄^*3H₂O) is a bright greenish-yellow pigment when manufactured, but has been reported to darken rapidly to a dull, ochre yellow hue. Most notably, this occurred in the late 19th century masterpiece <i>A Sunday on La Grande Jatte</i> – 1884 by French Post-Impressionist Georges Seurat. In order to shed light on the deterioration processes affecting this pigment, model systems simulating the composition of the paints of <i>La Grande Jatte</i> have been subjected to artificial aging under various environmental conditions (light, humidity and the acidic gases CO₂ and SO₂), in order to systematically probe critical parameters individually and in combination. Experimental results indicated key interactions, such as the important role played by relative humidity. The significance of this work goes beyond the specific study of a single painting and contributes to the overall study of chromate pigments.