I have a test tomorrow morning, so I've wanted to heat and practice stowing my bottle of QF so I was good to go tomorrow morning.

I heat it in the microwave for 10s, stopped, then another ten (it bubbled slightly at the end), but when I removed it, even though the bottle was quite warm, the temp strip read black.

So what is the best, cheapest way to work around this? Get a digital thermometer?

Just want to make sure I'm good to go - it felt quite warm, and my plan was to take it out of the microwave, rubber band the heating back to it, and stow it between two pairs of boxer briefs.

Sounds like youve overheated (bottle temp over 100 dg). Simply let the bottle cool down until you see the green indicator on the temp strip.

I agree. Sounds like it was too hot. Pour the quickfix into another clean container (make sure no sunlight around) and practice with water. I could get 100 degree "sample" to practice with straight from the tap, no microwave required!

I got a childs temp strip at walgreens for about $2 if your temp strip still fails to work.