The Ministry of the Interior had commissioned a number of reports into the availability of certain building materials, with the result that stones long not seen in Vienna were used, such as Wöllersdorfer Stein, for plinths and free-standing, simply-divided buttresses, the famously hard stone from Kaisersteinbruch, whose colour was more appropriate than that of Kelheimerstein, for more lushly decorated parts. The somewhat coarser-grained Kelheimerstein (also known as Solnhof Plattenstein) was intended as the main stone to be used in the building of the opera house, but the necessary quantity was not deliverable. Breitenbrunner stone was suggested as a substitute for the Kelheimer stone, and stone from Jois was used as a cheaper alternative to the Kaiserstein. The staircases were constructed from polished Kaiserstein, while most of the rest of the interior was decorated with varieties of marble.