Ring Marks In Black Granites
Strange Ring Marks & Acidic Stain Marks In Black Granite - PLEASE READ UPDATE BELOW
We have seen a very strange phenomenon in some pieces of black granite and that is a circular ring mark when viewed from a specific light source or direction.
To be honest we have absolutely no idea what causes this. When we first saw it we thought that someone had placed a very hot saucepan with a "boiled over" acidic juice on the pan bottom onto the worktop surface. On closer inspection and testing it was obvious that the worktop surface had not been damaged nor penetrated by anything therefore we recommend that trivets or mats should be used to avoid any possible marking.
It has been suggested that these ring marks are actually caused only on black granites that have had a sealant applied and that the ring has etched into the sealant. To remove this sealer one would have to use Methylene Chloride, usually found in paint stripper. EXTREME CAUTION should be used when using this solvent, be very careful and have adequate ventilation.
We have seen very positive results when a granite with a suspected sealant has been removed.
Why Do We Feel This May Be The Logical Explanation? Our Indian black granites have been quarried since the very early 1970s and we have produced tens of thousands of memorials and exported them to all different climes in the world. Insofar as we know none of these granites have had this problem nor failed and experienced stonemasons have always been able to restore the polish to a near-perfect condition when renovating the memorial and this is for a natural stone which has had to withstand the worst rigours that nature can throw at it.
It must also be remembered that applying sealants to granite countertops has only really been around since the late 90s and promoted heavily by those sealant producing companies and especially so in the U.S.A. Undoubtedly they can work extremely well on the more porous granites but we definitely have our doubts as to the value of using them on our black granites.
Furthermore, since we've mentioned the more porous granites, ripe raspberries and strawberries left on a worktop can cause staining so can citrus fruit juices and red wine and also vegetables such as beetroot plus there are also some bleaches and cleaners on general sale which we do not recommend applying to ANY natural stone surface.
To read the Marble Institute of America's recommendations about sealing stone, please go here.
REMEMBER that your worktop is a natural material and as strong and beautiful as it is, it is not impervious to a bout of stupidity!
UPDATE 22nd September 2010 Regarding Ring Marks
Calcium is in some varieties of absolute black. The rings are a result of some acidic fluid being on the bottom of a bottle or glass and the object is then set on the granite. The calcium will not migrate within the stone. The acidic fluid could have been coffee, soda, alcohol, Gatorade or literally of hundreds of other products that have a pH lower than 7 (which denotes acidic). A pH higher than 7 would be alkaline.
The calcium will react with any acidic solution, even very mild ones such as gatorade or soda.
The rings would be a result of the acid in any liquid that would accumulate around the base of a glass (round, circular, etc), not an organically, spontaneously generated calcium/acid reaction.
The rings are there as result of a direct action/reaction chain of events. The action was the likely introduction of an acidic solution (less than 7 pH) to contact the stone (probably in the form of liquid around the base of a glass). Whether the reaction is with the calcium or an enhancer, no permanent solution is available, as far as is known.
© Copyright Eurasian Natural Stone 1st December 2009 - Updated 22nd September 2010