Catherine Dewey, who is a regional architectural conservator at the National Park Service, at Meridian Hill Park in Washington. (Matt McClain/FOR THE WASHINGTON POST)

I can tell you where almost every monument is. There’s over 200. It’s kind of all in my head, but we also have a database. It includes all of the structures, both monuments and architectural features, buildings — anything that’s a built feature. That gets reviewed every five or six years to determine the condition of something. And if we find that the condition is fair, that becomes a priority to work on it to make it good.

After having been in the field for a while, you learn most likely what will work. You have to know what kind of stone you have in selecting what kind of chemicals to use. Graffiti can be really, really challenging to remove.

As conservators, we still maintain what the artist would’ve intended. You wouldn’t paint over Michelangelo’s ceiling because you thought: The hand’s pointing the wrong way. Architectural conservation comes from art conservation: You’re doing your very best to maintain the image or the object as it is.

Sometimes you can’t do anything. There’s a monument downtown that had a lot of little cracks in it. At some point in its history, somebody dug out the cracks and filled it with an epoxy, which was harder than the stone. The epoxy was contracting and expanding and causing additional cracking, so a couple summers ago, I went and I removed all of the epoxy, and I put in a compatible material to fill in all those gaps. And they all turned gray. It’s a white marble, and they all turned a slight gray. In fact, one particular crack turned chartreuse. I was meeting my friend downtown, and I said, “Oh, let’s meet there.” And I’m looking at the statue, and she comes over, and she’s like, “It’s not supposed to be that color, is it?” I’ve tried different methods, and it hasn’t helped. On the other hand, the monument is now stable, whereas before it was actively deteriorating. Sometimes that’s all you can hope for.