A lot of work is put into the evaluation of synthetic materials for use in the conservation of all types of antiquities. The tests are carried out on each material in isolation, whereas materials are very often used in combination. For instance they are always in contact with at least a small section of the object as is the case for adhesives. This can lead to problems of accelerated deterioration if the adhesive and the substrate are reactive. In ceramics conservation filling and retouching normally involve a combination of synthetic materials. For a filling the repair will be made using a filler, possibly mixed with a color, overpainted with a material to simulate a glaze. The glaze material may contain powder, or other type of colorant, and a matting agent. In this paper accelerated yellowing of a repair to a hard paste porcelain figure is reported. The materials involved in making the repair were previously found to have reasonable light stability, and were therefore considered suitable for use in ceramics conservation. However when they were used in combination yellowing occurred very rapidly. The cause of the yellowing has been investigated, and identified by a process of deduction and experiment. -- AATA