Bee,
Great question! My 11 year old twins have been working on this skill. Even with fluffed up cotton balls they have trouble getting the cotton ball to light. The first problem they have is getting a good spark. As has been mentioned; either the scrapper is dull or they are not scrapping at a good angle to make sparks. Once they get a good scrapper and technique going their next problem is not getting the sparks close enough to the cotton ball. As has been mentioned you have to hold the scrapper and pull the ferro rod toward you. When you get ready to make the spark the scrapper has to be within ˝ inch of the tinder. My boys have worn out a few BS Hot Spark ferro rods working on this skill.
As a side note:
I went camping with my oldest son last weekend in northern Arizona. It was down to 32 in the morning. There was dew on the pine needles and leaves in the morning when I got up and wanted to make a fire. There was no dry natural tinder. But there was a pine tree stump near by. It was a natural stump that had split in an uneven way leaving fingers of fat wood sticking up. I was able to kick off some fat wood sticks. I took one and scrapped the side with a knife to make a half dollar size pile of pitch wood shavings. There was a small log in the fire pit. I placed a pitch wood stick against the log, sticking up. Then I put the pile of pitch wood shavings at the bottom of the pitch wood stick. Then I placed some more sticks against the log to form an A around the pitch wood stick. I was able to then use my County Comm Metal Match to make sparks to light the pile of pitch shavings. I use the back edge of the saw on my Leatherman Charge Ti as the scrapper. The fire from that set the pitch stick on fire. The fire from the pitch stick caught the other sticks on fire and I had a sustainable fire going with little effort; a kick, some scrapping and sparking. I did not use any natural fluffy tinder. Such things would have been wet. Northern Arizona does have what some people call “fire weed” that will catch a spark, if it is dry. For one handed use: stick the knife in the ground and scrape the fat wood and ferro rod against the knife blade.
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Thermo-regulate, hydrate and communicate.