Some how I lost my last Hot Spark and picked up a new one. The rod was coated with a thin layer of some sort of plastic. I was scraping it with the striker, and thought why not use some sand paper to get the plastic off? So I grabbed a sheet and started to remove the plastic, only to get sparks. I then grabbed the rod with the sandpaper and pulled the rod out there was a huge shower of sparks. I don't know if this is news to anyone else but I thought it was neat.

Take Care and Stay Safe

I just got a Hot Spark recently. I love it; It is a new favoite. In fact I just bought 4 more today since they are so cheap.
I didn't know about the sand paper I just use the back of my knife.

I use the BSA Hot Spark. Really good item for the price. A Hot Spark and a 35mm film canister of PJ cotton balls is always in my daypack.

Warning: Science content below (at least as well as I understand it)

The Hot Spark , the "flint" in your Bic lighter and other such fire starters are Ferrocerium. It is a mix of rare earth elements, iron oxide and Mg oxide. When you scrape it with a sharp object, you slice off a tiny bit of the ferrocerium that the friction causes to ignite to produce the spark.

I have never tired sand paper, but any sharp scraper should work. I have used the stainless steel blade of my SAK with a hot spark. A sharp rock, a sharp peice of glass or a stainless steel blade can work just like the striker that comes with the Hot Spark. If you lose the little steel striker that comes with the Hot Spark, you are not totally out of luck. ( I keep the striker tied to the Hot Spark with a short loop of cord.)

If you make a fire with real flint and steel, the flint shaves off a thin sliver of the steel. The friction ignites the steel to produce a spark. Since it is the steel that burns, a bit of carbon steel is a must in using real flint and steel.

With a Hot Spark (Ferrocerium) it is the shaving from the Hot Spark that burns. What you shave with can vary. With Flint and steel, it is the steel that burns. The hardnes and sharpness of the flint and the type of steel (carbon steel) are both critical.