There’s only one instance when the perceived problem corresponds to the actual problem in the stone world: When a piece of stone is broken.
In all other instances the perceived problem may correspond to the actual problem...but then again it may turn out as being something totally different!

You will (hopefully) remember that I briefly mentioned stains and “stains” on polished marble and travertine surfaces in my article in the last issue of this magazine... right?
I said then that it was a story for another installment and so, here it is now.

Stains and “Stains”
Let’s start by saying that a true stain is always darker than the stained material. If it is lighter it’s either a mark of corrosion created by an acid (etching) or a caustic mark created by an alkali, a.k.a.: base (bleaching).
There are no exceptions that I can think of to this rule.
A true stain is a stain, while etching and bleaching are “stains”, which in the case of natural stone are actual surface damages. (There’s seldom real bleaching possible with stone: only etching.)

That being said, if we see a spot darker than the rest of the stone, it probably is a stain (it may also be a natural discolouration in the stone itself). If the stain is either dull and of a lighter colour, or dull and of the same colour of the rest of the stone, it is not a stain - ever.

It is rather a “stain”, which means that it’s probably a surface damage. (It may also be a “dead spot” in the stone created during its formation. “Dead spots” have no crystals and therefore they will not polish. They are rare occurrences, however.)
So, if someone calls-in indicating that they have a “water spot” or “water ring” on their polished marble or travertine surface, we know that they’re not stains for sure. They are (in the vast majority of the instances) either etching, or (rarely) a natural flaw in the stone. (As said before, bleaching rarely happens on natural stone.) Further investigation will bring into the open that some pH active substance – mostly (but not necessarily limited to) acidic in nature – was spilled on the surface of the stone. E.g.: Contact lens cleaner; the puppy’s vomit; perfume; salad dressing; a drink (any drink, even most soft ones); a generic cleaning product not rated “for natural stone”; lemon or orange juice; and so on through a virtually endless list. All these “water spots/rings” are duller than the rest of the surface of the stone and are either of the same or of a lighter hue. The darker the stone is when polished, the lighter the “stain” will appear.

One will seldom receive a call about a true stain on marble or travertine.

A stain can be (easily) removed by poulticing it out. A “stain”, being an actual surface damage, can only be removed by restoration. On polished stone surfaces, in the majority of the instances a good-quality polishing compound will take care of the problem. With more severe etchings some light grinding (honing) before polishing may be required. Hone-finished surfaces will need to be re-honed. On natural-cleft stone surfaces, no repair is technically possible, but the “stains” can be hidden with a good-quality stone colour enhancer.

Sometimes it is possible to have a combination of both a stain and a “stain”. For instance, if one spills red wine on a piece of polished light-coloured marble and let it unattended for a long time, the acidity of the wine (acetic acid) will etch the surface of the stone on contact, and by doing so it will also open its pores.
This will allow the wine to get absorbed by the stone and actually discolour (stain) it. In a case like that, first you will have to remove the stain by poulticing the dark discolouring agent out from the stone, and after that you will proceed to refinish (restore) its surface.

And now that we’re done with the first myth: stains and “stains”, since I still have room before you get bored, we’ll go to another myth:

Scratches and “Scratches”
A scratch is a scratch, right? Not so quick!
It may indeed be a scratch, but then again it may be something totally different that looks like a scratch; or it could even be a combination of a scratch with something totally different.

Enter the phenomenon of “stunned crystals”.
Many true geological calcite-based marbles when undergoing a stressing event (a hit from a hard, blunt object; the sheer pressure exerted on a small portion of the surface of the stone by the high-spikes of a woman shoes; etc.) will make the calcite crystals of the stone kind of “explode” along their natural cleavage.

Such an “explosion” will create a dramatic expansion of the damaged crystal, which in turn will compress and stun the surrounding crystals in every possible direction, creating sort of a “Domino effect”. The visual result is a whitish spot that is going to be larger and deeper depending on the amount of stress and/or the size of the crystals. (The higher the pressure and/or the larger the calcite crystals, the more extensive the stunning is going to be.) There could also be some damage on the surface of the stone (nick), but it will turn out as being most of the time remarkably smaller than the visual damage, if any at all. If there was no stunning of the stone crystals, the nick would go probably unnoticed.

If somebody drags a heavy piece of furniture across a true geological calcite marble floor, it may scratch and stun the crystals of the stone. Or it may just stun them. This is the typical case when somebody rolls a grand-piano over a calcite geological marble floor, because the bronze wheels the grand-piano is sitting on will seldom actually scratch the stone surface, but they will definitely stun its crystals often to a depth that no grinding procedure will ever be able to reach.

All the weight of the grand-piano is concentrated on the three tiny metal spots in contact with the floor! The case of a grand-piano is so extreme that even certain compact limestones and travertine will stun! However, due to the small size of their calcite crystals, the stunning on those stones is rarely deep to the point that it could not be repaired by grinding them.

Is there any way to repair stunned crystals?
Hardly.
As indicated before, only light stunning could be removed by grinding; but if the stunning is deep enough there’s no practical hope.
Getting to know as many of the different stones on the market as possible, and being able to classify them geologically is what separates true stone restoration professionals from stone restoration contractors that can only claim hands-on experience.
That’s all for now, folks!
I ran out of space again.
But stay tuned: the next time we’ll talk about three more stone myths. All exciting stuff, I promise!