Cleaning the Capitol Dome

For six weeks this summer the Michigan Capitol was inundated with clinking, clanking, and hammering as almost 160 feet of scaffolding was constructed in the rotunda. Visitors, legislators, and staff watched fascinated as this immense and intricate tangle of metal grew from the glass floor all the way to the oculus. Then, as workers put the last pieces of scaffolding into place in July, the rotunda suddenly fell quiet. Since then, every guest who walks into the building has asked – what are they doing up there? 

The scaffolding was constructed so contractors could repair the badly damaged decorative paint in the interior of the dome. But, before any of the damage could be addressed, or any new paint applied, every surface needed to be cleaned. Guests often comment on the cleanliness of the Capitol’s public spaces, but the folks who admire the shine on the floor tiles would be shocked at the state of the dome. While Capitol staff occasionally clean the areas of the inner dome they can reach, there are many spaces that are inaccessible without having a scaffold in place. The last time the entire space was thoroughly cleaned was over 30 years ago during the Capitol’s restoration. 

In addition to three decades of dust and dirt buildup, there are also stains left by condensation that formed between the inner and outer layers of the dome. While the gaps where condensation collects could be sealed with caulk, the Capitol’s preservation experts fear that the caulking would reach the end of its lifespan and fall apart long before another set of scaffolding would be built in the rotunda. The hope is that the measures taken during the Capitol’s Infrastructure Update to improve the weatherproofing of the dome’s exterior will prevent condensation issues in the future. 

Before the cleaning began, the entire scaffolding was wrapped with a sheer, black fabric. This will act as a safety net, protecting the Capitol’s occupants from dropped tools or falling debris. It also discourages some of our younger visitors from reaching out to touch the ‘jungle gym’. With this protection in place, decorative painters with the John Canning company started with a dry cleaning, working from the top of the dome down, they used paint brushes and vacuum to lift away loose dust. 

The next step was a wet cleaning, using water to remove more stubborn stains and dirt. Surprisingly, the original paint applied to the Capitol’s interior was not water safe! The decorative painters working in the 1880’s used distemper paint, made from pigments mixed with a binder such as animal glue. By the time the dome was restored in the 1990’s, painters were using oil and acrylic paints which are much more durable. 

While cleaning may not seem like the most exciting task, it is a vital and sometimes transformative step in the conservation process. As the dome’s lovely art emerged from layers of grime, contractors could assess the condition of the paint and form a plan for its repair. By the fall of 2023 they were starting to examine colors, remove loose paint and replicate damaged designs. We will be returning here soon to share this captivating process now that the dome is freshly cleaned for another few decades.