+1 on the respirator. Some compounds have silicon in them & steel powder is not the best thing to inhale as you've found :)
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The buffer is the most dangerous tool in the workshop. I know of knifemakers who had chain mail aprons made just for working on the buffer.
Brownell's has some compounds (555 series) that are good quality and get the job done. I've used greaseless compounds for years and they are really good, but some companies use a horsehide glue base and I do not recommend leaving those at room temperature. First, they will turn into a useless puddle, second, you will not believe the smell.