Alfred Maudslay visited Palenque in 1891 for the purpose of photographing and making illustrations of the ruins. One of the tasks in the monumental labor was to clean the stucco modelling on the piers to prepare them for being photographed. This was a work that could not be entrusted to others, as it needed not only great care but also some knowledge of the designs being uncovered.
[Maudsley writes:] "In some instances these decorations have been preserved in a very curious way: the water continually dripping on them from above has passed through the dense mass of decaying vegetation which covers the roofs of the buildings, and has become charged with carbonic acid in the process; it has then filtered through the slabs of which the roof and cornice are built, dissolving some of the limestone on its way, and redepositing it in a stalactitic formation on the face of the piers.
Mr. Price and I worked for some weeks at clearing the carvings of this incrustation, which varied from a hardly perceptible film to five or even six inches in thickness. The thinner parts were the more difficult to deal with, as they were exceedingly hard; where the thickness exceeded two inches a few taps with a hammer would sometimes bring away pieces two or three inches square, and we were fortunate sometimes in finding the colours on the surface of the stucco ornament underneath still fresh and bright."
They found it necessary to wear glasses to protect the eyes from the hard, flint-like particles that flew off at the blow of the chisel.
"Progress with the thin incrustations was sometimes so slow that only a few square inches could be cleaned in a day. In other cases the attempt at cleaning had to be given up altoghether as the filtration had formed a hard crust whilst the stucco beneath had become disintegrated and soapy, and had no surface left. [But when, in other cases,] the incrustation could be removed in large pieces and the surface of the stucco was sound, we sometimes found the colours with which it had been painted still retaining something of their former brilliancy."
Ian Graham, Alfred Maudslay and the Maya, p. 175-6