It's useful to be able to edit a material in the Material Editor and have it immediately updated in the scene. Sometimes you want to work on a material without affecting the scene. You want to adjust a material until you're sure that it's what you want, and then reassign it. In other words, you want to cool a hot material.
You cool a material by copying it in the Material Editor sample slots. You can copy a material in two ways:
When you drag to copy a sample, you end up with two materials with the same name, but one is cool while the other is hot. In the Material Editor, you can have up to 24 materials with the same name, but every material in your scene must have a unique name.
You can now adjust the cool material, and compare it with the hot material. If you like the changes you've made, you can update the scene.
