Gotland's medieval churches often have beautiful murals inside the church, but not many people know that the outer portals were also painted in the Middle Ages. Unfortunately, only faint traces of paint remain today on a few churches. These traces of paint have never been analyzed before. It is therefore both urgent and urgent to perform chemical analysis on these medieval pigments, before they have completely disappeared. The churches we intend to investigate are located in the parishes of Martebo. Bro, Källunge, Garde and Lye. Martebo church in northern Gotland is the most interesting. Its beautiful limestone portals and capitals (with carved pictorial suites) were made by "Bygghyttan Egypticus" in the 14th century. Although the rest of the church building shows clear signs of weathering and biological growth, the capitals are unusually well preserved. Some of the churches' limestone capitals have a yellowish color, which may explain why they are still in such good condition. Therefore, the yellow color should of course be chemically analyzed. The structure of the limestone and the toxic color pigments (acting as biocides) may also have contributed to its preservation. Our multidisciplinary research group aims to solve these problems. It consists of experienced chemists and conservators with backgrounds from the Nordic Museum, the Swedish National Heritage Board and the Byggnadshyttan Foundation on Gotland.