When to heat oil in dutch oven? I have an enameled cast iron dutch oven.  I thought the pamphlet that came with it said not to heat the cast iron dry -- I could be imagining things, though.

Part One

So, am I supposed to put the oil in the dutch oven and then put it on the (cold) stove and then turn on the stove to low heat and then to medium?  If I do this, will the oil evaporate -- I thought I experienced that once?

Or am I supposed to preheat the dutch oven (starting on low and then going to medium) and then throw in the oil and heat it?

I'm asking this question because I don't want to ruin my le creuset french oven.

Part Two

And how do you know when the oil is hot enough?  This recipe says until it is almost smoking, but how do you know when it is about to smoke?  And don't all oils have different smoke points.  This recipe calls for vegetable oil, which I assume can be canola.
Part one:

Yes, put oil in first then put on a low/med heat.  Generally cast iron should be heated gently,  depending on your stove it should probably take about 5 minutes to get to a good temperature.  The oil shouldnt evaporate - I've never experienced this.  As to the type of oil - I use various depending on circumstance vegetable or olive usually.

Part two:

I generally shake the pan gently - when the oil becomes more less viscous (more runny) then it is at a good temperature to start cooking.  You can also put something like a small piece of onion or bread into the oil - if it starts bubbling and generally cooking then its good to go.  Some people use a couple of drops of water to see when it spits but I dont like doing this partly due to the safety factor and also due to the fact itll splatter over the stove top.

It depends a little on what you are cooking - if you are looking to brown some meat for example you'd probably want it a little hotter than if you were just going to make vegetable soup.