Both the plastic bottle of water and the plastic baggy filled with water will work in a pinch, but it is much easier with a magnifying glass. I have done it with water, never with urine, though it is good to know that will work in an emergency.
For me, learning to use a bow drill took a lot of time and patience and then frustration when I ran out of patience.
It's kind of like riding a bike, once you achieve and the muscle memory is learned it gets much easier to do. Somewhere in my files, I have a page that shows the color and condition of the dust and what it should and shouldn't look like in order to get a coal. I will look for it and post it here when I find it.
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“You’re so hard on yourself. Take a moment. Sit back. Marvel at your life: at the grief that softened you, at the heartache that widened you, at the suffering that strengthened you. Despite everything, you still grow. Be proud of this.”