The Copenhagen Opera House (Operaen) is the national opera house of Denmark, and among the most modern opera houses in the world. The building was designed by architect Henning Larsen in close and often problematic collaboration with Mærsk Mc-Kinney Møller. Mærsk wanted to the building to have several features in its design: it would not become obsolete in function and appearance due to any fiscal compromise. He personally tested seats and materials, he visited many places in the world to see how opera buildings were constructed and how the building materials were looking after having been exposed over time to weather. Henning Larsen, on the other hand, was trying to make sure that the original architectural ideas were carried through the construction process, especially concerning the large glass surface front, which became a matter of great controversy and subsequent compromise. The building exterior is faced with Jura Gelb limestone and situated on ground that is surrounded by canals that are designed to give the impression the structure is on an island. The bridges constructed to access the building were made from oak trees originally planted in the 19th century for use in replacing the national fleet that was lost with the bombardment of Copenhagen in September 1807. The front of the building was originally designed with large glazing panels in order to see the shell of the auditorium from the harbor side. However, Mærsk emphasized that glass does not age well, so the façade was changed to a metal grid. The foyer floor is Sicilian Perlatino marble. The central foyer holds three spherical chandeliers created by the Icelandic artist Olafur Eliasson. Each chandelier consists of several pieces of glass, which are semipermeable allowing some light to pass, and some to reflect. The patterns change when viewed from different angles. Per Arnoldi designed the logo for the opera, visible in the marble floor just inside the entrance, and Per Kirkeby created four bronze reliefs for the wall to the auditorium, just below the maple wood part. Per Arnoldi also designed the Front curtain for the main stage, made of multiple color threads creating a three-dimensional effect, that does not reproduced well in photographs. The rear wall of the foyer and balcony faces are maple. The architects' original intention was to make the wood look like that from an old violin. However using the same technique would have been far too expensive. Instead, they have tried to imitate the color using more traditional staining techniques, and the result is very close (the official homepage says differently, but the guides in the Opera tell this story). Due to the orange color and its form, it is suitably known by locals as the pumpkin. The auditorium ceiling is gilded with about 105,000 sheets of almost pure carat (100%) gold leaf; 24 carat (100%) would not stay applied sufficiently. The floor in the main auditorium is smoked oak. The balcony faces have been designed with openings in a special pattern to improve sound quality, and LED-based lighting that can be illuminated in a variety of patterns.