Hey there,
Charts are just pictures it could be of anything and everything we just need to study it. It could be a chart of oil, stocks, gold, unemployment, crime, sound or anything for that sake and the deep study is technical analysis. That means for TA you just need a valid chart with an appropriate timeframe. To answer ur question yes Technical Analysis do work for commodities and if u didn't knew that fact how were you giving those calls.
Cheers
G-unit