he encouraged his students to copy his paintings, sometimes finishing or retouching them to be sold as originals, and sometimes selling them as authorized copies. Additionally, his style proved easy enough for his most talented students to emulate. Further complicating matters is the uneven quality of some of Rembrandt's own work, and his frequent stylistic evolutions and experiments. As well, there were later imitations of his work, and restorations which so seriously damaged the original works that they are no longer recognizable. It is highly likely that there will never be universal agreement as to what does and what does not constitute a genuine Rembrandt. Painting materials Technical investigation of Rembrandt's paintings in the possession of the Gemäldegalerie Alte Meister and in the Gemäldegalerie Alte Meister (Kassel) was conducted by Hermann Kühn in 1977. The pigment analyses of some thirty paintings have shown that Rembrandt's palette consisted of the following pigments: lead white, various ochres, Vandyke brown, bone black, charcoal black, lamp black, vermilion, madder lake, azurite, ultramarine, yellow lake and lead-tin-yellow. One painting (Saskia van Uylenburgh as Flora) reportedly contains gamboge. Rembrandt very rarely used pure blue or green colors, the most pronounced exception being Belshazzar's Feast in the National Gallery in London. The book by Bomford describes more recent technical investigations and pigment analyses of Rembrandt's paintings predominantly in the National Gallery in London. The entire array of pigments employed by Rembrandt can be found at ColourLex. The best source for technical information on Rembrandt's paintings on the web is the Rembrandt Database containing all works of Rembrandt with detailed investigative reports, infrared and radiography images and other scientific details. Name and signature "Rembrandt" is a modification of the spelling of the artist's first name that he introduced in 1633. "Harmenszoon" indicates that his father's name is Harmen. "van Rijn" indicates that his family lived near the Rhine. Rembrandt's earliest signatures (c. 1625) consisted of an initial "R", or the monogram "RH" (for Rembrant Harmenszoon), and starting in 1629, "RHL" (the "L" stood, presumably, for Leiden). In 1632, he used this monogram early in the year, then added his family name to it, "RHL-van Rijn" but replaced this form in that same year and began using his first name alone with its original spelling, "Rembrant". In 1633 he added a "d", and maintained this form consistently from then on, proving that this minor change had a meaning for