A number of emails have come into my inbox from curling television fans who have noticed on closeup shots of curling stones that there's a line etched into the circumference of the stone parallel and about a centimetre or two from the "striking band". It's called the "score line" and it was placed there when the stone was manufactured and here's why.
If one removes the plastic cap from a curling stone and the bolt that holds it in place, one will discover that a curling stone is perfectly symmetrical. When it's "naked", it has two running surfaces. In other words, a stone can be flipped over and it will respond as any curling stone might. In the "old days", when curlers still used actual curling brooms (can you imagine that, oh wait, that's what I used, yikes) most all curling stones were "homogeneous" (my word, not that of a curling stone manufacturer so my apologies to "Canada Curling Stone", "Kays of Scotland" etc.). In other words, the stone was formed from a single piece of granite, kinda like "single malt scotch" (and I don't even like scotch). When a set of curling stones arrived at a curling club, spankin' brand new, the handles were attached so that the "score line" on each stone was either above or below the striking band.
Over time, the ice technician might decide to turn/flip the stones so that the other running surface might get some "ice time". Well, this flipping could get confusing if there was no way to tell top-from-bottom. Without a handle or cap there would be no way to tell if a stone had been flipped. The score line removed that doubt.
In those same "old days" when most curlers employed a back swing delivery, the ice technician would regularly rotate the stone relative to the position of the handle so the same point on the running surface was not coming into contact with the ice when it literally struck the surface on the down swing and some down swingers really made the landing of the stone an adventure. With today's no back swing delivery, I doubt whether any ice technician does that any longer.
Most curling stones manufactured today are not "homogeneous". They are composed of two types of granite and are known by the term "insert". The shell of the stone is likely to be a type of granite known as "trefor" while the portion of the stone that actually touches the ice is "blue hone" granite which has been inserted into the trefor shell. Trefor granite makes for great striking bands while blue hone is ideally suited for running surfaces and will last, well, much longer than anyone reading this post. Although there is another running surface under the cap, it's not destined for use. So, I guess a score line for an inserted stone is really not necessary but many inserted stones are stones that started their curling life as homogeneous and the score line was already there.
And that's how many curling stones are made today. One of the manufacturers will take the blue hone curling stones a club might have and retrieve three "insert" cores. The manufacturer will then core out the bottom of a set of trefor stones and voila, that lucky curling facility has the best of both worlds and the curling stone manufacturer has two more inserts ready to be placed (by epoxy adhesive) into more trefor shells.
This "Season of Champions" we've been hearing a lot about "lively rocks". It's not exactly the rock material (i.e. the granite) that makes rocks lively, it's the profile of the striking bands. When stones are "new" the striking bands (they appear a lighter shade of grey [no ladies, we're NOT taking about "Fifty Shades of Grey" so settle down]) are somewhat "convex" (get your dictionary out, you remember dictionaries, the books with all the words and their meanings). As a result, the stones have little actual striking surface and therefore "bounce". As those striking bands wear down, they flatten out and become wider. As that occurs, they become less lively!
Now, in the face of all that's been happening in our world of late, aren't you glad to have all this "useful" information about curling stones! But if it's more you want, the Canadian Curing Association has, on its web site (www.curling.ca) an excellent video on taking the mystery out of curling stones. As curlers, we need to learn as much as we can about our playing environment. The more you know about it (ice and stones) the better you will perform!
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