I did a little experiment to try and get the average % of each temper from refining raw ore (I didn't do this with cloth, hide, or wood yet). This will also include the overall chance of not getting a temper too.
I did 10,000 Voidstone Ore, in 2 sessions of 5,000 each. (500 refines each session)
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Session 1:
-8/500 Tempering Alloys
-39/500 Grain Colvents
-63/500 Dwarven Oils
-71/500 Honing Stones
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Session 2:
-15/500 Tempering Alloys
-48/500 Grain Solvents
-65/500 Dwarven Oils
-73/500 Honing Stones
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Approximate % of 1000
-2.3% Tempering Alloy
-8.7% Grain Solvent
-12.8% Dwarven Oil
-14.4% Honing Stone
-61.2% No Tempers
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So approximately 2 of every 5 refines should give a temper, etc, etc, you guys can interpret this I'm sure.
I actually thought the chances per temper felt much higher when I was actually refining the Voidstone.
It should also be noted that the ore quality may have an effect on the overall outcome. For example, higher quality ore may yield Tempering Alloys and Grain Solvents more often. I think that is unlikely, but it's possible. I may redo this with Iron Ore at some point, if I feel like getting 10,000 of it...