Even after all the years I have been in the stone business, the mysteries and problems I run into on a regular basis never cease to amaze me. Today would prove to be one of those days.
I was enjoying a cup of joe at my local greasy spoon, talking to Marge the waitress, when my cell phone rang. I checked the caller ID and didn't recognize the number. I usually let it go to voice mail but I had a funny feeling I should answer this call.
"Mr. Stone Detective?" the scratchy voice asked. "We just fabricated a kitchen with Sienna Bordeaux, and several days after we installed it, the customer called and said the edge has this bluish-green stain on the edge (see picture) and we have no idea what is causing it. We have tried every poultice imaginable to remove the stain and it's not coming out. Can you please help us?"
Like any good forensic investigation I put on my Colombo personality and proceeded to ask some questions.
"What diamonds did you use to profile the edge?" I asked this question because sometimes the resin from certain diamonds can bleed into the stone. "Did you use any treatments on the stone? Sometimes you can get some adverse reactions with certain sealers, enhancers and so forth." Every question I asked, they came back with an answer that didn't add up to a green stain, in my book. I next asked if they used any glues or adhesives. He told me that they used CA glue (Cyanoacrylate) for small repairs.
"Ok," I said, "now I have all the information that I needed to start my investigation." What was strange about this call is that I had received a call similar to this a few months ago, but never had the opportunity to investigate it. I asked if he had a picture of the staining and he said he would email it to me. I finished my cup of joe and conversation with Marge, then headed back to the office to check my email.
On the drive back, I kept going over and over in my head what could have caused this staining. In my years of stone forensic investigations I have found that too often I am not told the full story. In other words, many times I am not told everything that was done to the stone. But in this case the only thing that seemed suspect to me was the CA glue. I couldn't wait to look into this further.
I got back to the office and logged on to my computer. The familiar voice immediately chimes in with, "you've got mail." I opened the attachment to examine this bluish-green stain. The discoloration didn't seem to be something that resin in the diamonds would cause but looked the color of copper when it oxidizes.
My first gut reaction is that the stone had an unusually high content of copper which started to oxidize. My next step was taking a closer look at the chemistry of the CA glue. What I discovered was interesting.
For those of you who have never worked with CA glue for repair, the process is two steps. The CA glue is applied and then an accelerator spray is used to cure the glue. When I took a look at the accelerator, I discovered that it contained a chemical known as Quinone.
Now, for you non-chemists out there, let me tell you that Quinone is a chemical that is commonly used for both natural and artificial dyes. The most popular color dye for Quinone is blue.
Bingo, I thought. So I set up several experiments to test my theory. Sure enough, of all the accelerators that I used, the ones with Quinone turned most of the granites I tested blue.
Mystery solved, but how can the color be removed? I attempted several poultices and discovered a poultice of methylene chloride did the trick. Sometimes it pays to know chemistry!
The Stone Detective is a fictional character created by Fred Hueston, written to be entertaining and educational. Frederick M. Hueston is the founder of Stone Forensics (stoneforensics.com), a nationally known stone consulting company, and also the technical director for Stoneandtilepros.com. He has written over 33 books on stone and tile installations, fabrication and restoration. He also serves as a expert for many legal cases across the world. Email comments to him at fhueston@stoneforensics.com
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