Most important to the value of an artwork is the importance of the artist who produced it. For example, the general consensus is that Pablo Picasso is one of the most influential artists of the 20th Century, due to his many artistic achievements, including co-founding the Cubist movement with George Braque. A portrait by Picasso, therefore, can easily fetch many millions whereas a portrait by an unknown contemporary artist can have as little value as a couple of hundred dollars.
There is the visual impact of the work to consider. Stormy seascapes are generally less popular than calm seascapes. Some artists were better at portraiture than at landscape painting, and as a result their landscapes do not command as high a price as their portraits do. Materials and size matter. Oil paintings are considered more valuable than works on paper. Generally speaking and up to a point: the larger the work, the higher the price.
The condition of an artwork has a significant impact on its value. For example, if an artwork was pierced in an important area (i.e. the face of a portrait) then this will reduce its value more than damage towards the edge of the painting. If the work has been restored aggressively, this may significantly reduce its worth: the trade (i.e. dealers) favor untouched over highly restored paintings. When buying a valuable artwork it may be a good idea to obtain a second opinion from a conservator who will examine the work under UV light, revealing old restored areas and overpainting.
An artwork is a difficult asset to appraise. Although collectors can access auction data for a particular artwork online, it is important to keep in mind that these numbers usually do not tell the entire story nor do they reveal the drivers of value as discussed above. This is an excerpt from the ebook 'Art the New Asset Class' written by Annelien Bruins.