Rembrandt's own studio practice is a major factor in the difficulty of attribution, since, like many masters before him, 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.