Expert Metalwork Revealed in Restoration of the U.S. Capitol Dome

Restoring the U.S. Capitol Dome is a massive project. It's exciting to uncover the artistry of a long-gone era and to see elements of the Dome that have not been seen for decades.

More than 1,300 cracks in the nearly nine million pound cast iron Dome are being repaired by experts working day and night on the Dome scaffolding. But the Dome also has many ornamental and functional cast iron parts that are so broken and badly damaged that they cannot be repaired on site.

There are scores of decorative ornaments on the Dome – such as, scrolls, flowers, acorn finials, acorn pendants, rosettes, acanthus leaves. They were created in the 1850s and 60s and some of them are missing or damaged beyond repair.

A foundry in Salt Lake City, Utah, is recasting these pieces, and last week I had an opportunity see firsthand how the work is done.

Here is the process step by step:

• We select a piece of a cast iron feature that is in good condition, so it can be used to develop a pattern to cast a replacement.
• We remove these pieces from the Dome and ship them to the foundry where they can be used to create patterns for sand casting.
• The patterns are slightly larger than the original to allow for the shrinkage (1/8” per foot for cast iron) that takes place during the casting process. All measurements need to be absolutely exact
• The pattern is placed in sand with a chemical binder to create a mold. The sand mold cures in a matter of minutes and becomes as hard as sand stone. 
• Molten cast iron heated to more than 2,500 degrees is poured into the mold. This is something that is quite dramatic to witness!
• Once the mold is cool, the hardened sand mold is chipped away and a new ornament is revealed.
• The new ornament is shipped back to the U.S. Capitol and installed on the Dome.

Attention to detail and historical preservation are paramount. The careful process even allows us to reclaim some of the original cast iron, saving the historic fabric and reusing it in the ornamentation.

What I find most fascinating is the amount of detail that went into crafting the ornaments. It is incredible to see the intricacy and to realize that these decorations were created at the time of the Civil War. There are little lines and indentations the size of your pinky fingernail that cannot be seen from the ground and that have been obscured under a dozen layers of paint. It is astonishing to know that we are seeing these details for the first time since the last restoration in the 1960s.

It's an honor to be preserving American history and know that we are making it possible for the public to appreciate the skilled craftsmanship and artistry that are a part of the U.S. Capitol.

Learn more about the U.S. Capitol Dome Restoration Project at aoc.gov/dome.

Image	Image
Wood toolings are made using 3D scanners and automated cutters.	A wood tool is made of an existing rosette ornament. This negative will be used to create a pattern that will be used to make an impression in the sand molds for casting.

Image	Image
A tool made of rubber is made of an existing lambs tongue ornament. This negative will be used to create a pattern that will be used to make an impression in the sand molds for casting.	A newly cast lambs tongue ornament.