Rainbow "Stains" on Absolute Black Granite Counters
I have "Absolute Black Premium" granite countertops that have rainbow "stains" around the sink areas in my kitchen (I have two sinks...the "rainbow" is around both sinks).
The rainbows are primarily around the top of the sinks as well as around the faucet & soap dispenser holes.
I tested our stone for dye/doctoring as well as performed the lemon juice, red wine, & vinegar tests prior to purchasing and installing it and nothing affected it...so I'm 99.99% sure it's not doctored and that it is indeed AB granite.
No one seems to know what the rainbow is...including the fabricator...they say they've never seen it before and it must be the stone...but the rainbows are ONLY around the sinks and the faucet & soap dispenser holes, so I'm skeptical. (Unfortunately, they were fairly incompetent at fabrication & installation, so I don't trust them anyway.)
The sink cutouts were cut & polished at the fabricator while the faucet & soap dispenser holes were cut on-site during installation.
Can you help me????
Soap and some oils can create such a rainbow pattern. Why it is staining is a mystery unless soap and/or soapy water is left on the surface for long periods.
Of course, around the sink and soap dispenser is where you'll always find the greatest concentration of soap and soapy water.
Remember, AB can be very stain-resistant, but if something is left on the surface of any stone or any type of surface long enough, it could stain.
I'd suggest soaking and cleaning the granite countertops with acetone and a stiff, but soft-bristle brush and see if that helps.The other possibility
is that this is the result of the excessive heat that develops from cutting out the sink and faucet holes in the granite countertops.
You noted that the sink was cut at the fabricators. Most likely it was on a machine, which provides water cooling to the granite countertop, but it could have been done by hand where cooling may have been insufficient.
Or it's just the way your particular slab behaved. Even with water cooling the granite gets hot and the heat can change the minerals in the stone.
Rainbow Stain on Black Granite
by Jim Flannery
Black granite countertops...rainbow stains around the sink. How can these stains be removed. Thank you.
These rainbow-like stains on black granite countertops are a bit of a mystery. Definitely see them predominantly on black granite most likely because of the mineral makeup, the black color and light reflection.
These could be from a soapy or oily film or it could be due to changes that occurred with the minerals from the heat of cutting out the sink if done by hand.
Usually machine cuts are adequately cooled. If from heat there's not much you can do.
I'd suggest treating this as an oil stain and follow the directions for cleaning granite countertop stains in the Removing Granite & Marble Stains e-book
You may also try using methylene chloride on the surface, which will strip any chemical or residue from the stone.