Frederick M. Hueston, PhD

I was driving across the desert from Las Vegas to LA for an inspection and had to stop for a minute. I pulled into the rest area, did what I had to do and starting walking back to my car, when something in the distance caught my eye.  I looked out onto the desert and saw what appeared to be a small body of water. I started walking toward it, and when I had walked about 100 feet it disappeared. I have heard of mirages, but have only seen the one in Vegas. Well, this was no casino and it just happened it would be a clue to solving the mystery I was about to see in LA. I got in the car and continued my drive, occasionally looking across the desert for another mirage or perhaps I could catch Wile E. Coyote chasing the Road Runner.

When I arrived at the building downtown, it was still under construction and parking was almost impossible. It was a tall office building clad in a dark blue granite. I found a place to park in what looked like a seedy area, but who cares – the car was a rental and I had insurance. I grabbed my inspection kit and headed inside.  

I was greeted by a short, stout individual wearing a hard hat. The guy was a dead ringer for Danny DeVito. I was half tempted to ask him to call me a cab, but I resisted the pun. He handed me a hard hat and told me to follow him.

We entered an area behind a temporary plywood wall. He pointed to the floor and said, “There’s da problem.”

The floor consisted of a white, large-format porcelain tile. I looked down at the tile and didn’t see anything wrong. The layout looked good, the grout was in good shape, and the finish on the tile was consistent. I turned around and gave him a puzzled gaze, shrugged my shoulders and said, “What’s the problem?” 

This is a properly laid floor of high-end, large format tiles, with no actual lippage. So what’s going on here?

This is a properly laid floor of high-end, large format tiles, with no actual lippage. So what’s going on here?

He told me to walk across the floor to the other side of the lobby and then look. So, I walked to the opposite end of the lobby, turned around, and there it was. Along the perimeter of each tile was a dark smudge line. Interesting, I thought to myself. I set my eye on one tile and slowly walked toward it. Just as I approached it, the smudge mark was no longer visible.  I turned to Danny and said,
“OK, I’m no Renaissance man but I see the issue now.” Not sure he got the pun. I told him to stand in the very spot I was in, and asked him if he had a halogen light. He pointed up against the wall to where one of those halogen construction lights was clamped to a floor stand. I placed the light a few feet from the tile in question, walked back a few feet, and couldn’t see the smudge. I asked him if he could see the smudge from where he was standing and he said, “No, it’s gone!”

I smiled and told him he was seeing a mirage.  He seemed to get a little bit upset, but before he blew his top I said, “The problem is so common it’s even got a name: Optical Hazing.”

I explained to him the angle of light from the windows is casting a shadow on the tile. He shook his head and told me, “NO, the floor is perfectly flat with no lippage.”

I told him I knew. I motioned for him to come over and I took out my field microscope and placed it on the tile. I focused in and showed him that this type of porcelain had these tiny, microscopic pin holes. When the light hits these tiny holes at a certain angle, the light reflects off it, giving the hazing illusion he was seeing. 

“So how do we correct it?” he asked.

I told him there are several options:

1. He could tear it up and replace it with a different tile.

2. He could coat it with a thin coating. This will fill the holes and the light will reflect differently.

3. Sometimes polishing the tile to a higher shine may also work.

4. Change the lighting, or introduce more lighting, if possible.

I told him I would send him some details. I shook his hand and headed out to see if my rental car was still there. 

Another case solved – now back to the real Mirage on the strip in Vegas, to try my luck at blackjack.


The Stone Detective is a fictional character created by Dr. Frederick M. Hueston, PhD, written to entertain and educate. Dr. Fred has written over 33 books on stone and tile installations, fabrication and restoration and also serves as an expert for many legal cases across the world. Fred has also been writing for the Slippery Rock for over 20 years. 

Send your comments to fhueston@stoneforensics.com.