The part of the stone that actually touches the ice is called the "running surface" and it's exposed granite, much like the "striking bands". If you turn a curling stone over and run your finger around the running surface, it's going to feel "rough" in relation to the polished part of the stone. That roughness touching the pebbled surface while the stone "rotates" is what makes the stone move from right-to-left (counter clockwise) or left-to-right (clockwise) as it makes its way down the ice. That movement is why the game is called "curling".
The amount of curl is critical to the playing of the game from both a competitive aspect as well as an enjoyment aspect. It's simply no fun to play when the stones do not curl. Yes, you might as well play shuffleboard if that's the case! So clearly the ice technician's main responsibility is to make ice that allows curling stones to curl. But it's not just the ice that allows for the "curl", the rocks, or more precisely the running surface of the stones also plays a key role. To ensure that the running surface will "grab" the "pebble " sometimes the running surface will be "enhanced" (the preferred term for ice technicians). That running surface enhancement is the subject of this posting.
For all we hear about running surface enhancement, it's a surprisingly simple process. All one needs is a supply of "emery paper", kerosene, some clean cloths and of course the curling stones. Oh yes, I forgot one thing, a measure of expertise gained from experience with this process.
The stone is placed on one end of the emery paper with the ice technician positioned behind the emery paper. With the handle of the stone at the 10 o'clock position the stone is pulled toward the ice technician (to the opposite end of the emery paper). When the stone reaches its destination it's lifted from the emery paper and repositioned so the handle is at the 2 o'clock position. The stone is then pushed along the emery paper to its original position.
The key element in this pull/push movement of the stone is "equal pressure" on the entire running surface. That's the skill & experience part! Sometimes the emery paper is placed into a wooden frame which limits the movement over the emery paper to ensure that each stone receives exactly the same distance over the abrasive surface.
The photo below shows the path a curling stone took along the emery paper. The travel distance is about 10 cm. in both directions then the stone is lifted from the emery paper. The running surface is cleaned of any "granite dust" by a cloth which has been dipped in kerosene. Kerosene evaporates very quickly.
Ice technicians use one piece of emery paper per stone so the grit (the roughness of the emery paper) is consistent from stone to stone. Emery paper has the appearance of sand paper but the grit of emery paper is minute stone particles called emery and is native to Turkey (the things you find out when you do your homework) not silica (sand particles) and is usually cloth backed as opposed to paper.
Papering of curling stones to enhance their performance is temporary. Under normal conditions in a curling facility its effects will be noticeable for approximately 4-6 weeks. If the stones were to be "repapered", the handles might be positioned at the 12 & 3 o'clock positions so the cross hatching of the emery paper is somewhat different from the previous papering process described above.
If you're informed at your curling facility that the stones have been papered/enhanced, expect them to not only curl more but to break late. Don't panic if that's not the type of stone reaction to which you've become accustomed. Embrace the new conditions! That's why it's called "curling" and consider yourself and your club mates fortunate to have an ice technician willing to put the curl back into curling!