Basically you put some water into a condom and tie the end. Then you manipulate the condom to form a lens shape.
Once you get the shape correct the result is instant. Personally I favour Crampball Fungus for this method of firelighting.
I manage a nature reserve, teach natural living/wilderness living skills and own a cabin in Swedish Lapland (150kms inside the Arctic Circle). www.naturallore.co.uk
Personally I found this quite difficult and certainly much more work than the other type of woven baskets I have made.

After the first frosts of the autumn, the moss produces clusters of yellow spores which you can see above. These spore clusters are collected and after being left near the fire overnight, they open and release large amounts of spores.
When the spore powder is poured onto a naked flame, they produce a very explosive effect as you can see here......
and Cattail dolls