If you plan to use it at the forge, you might want to test the fabric for melting in an unobtrusive spot. :[
Good idea. I have a melters jacket from when I worked in the steel mills and it is 80% wool. I don't know what else is in it. It did not show signs of melting around the arc furnace which was running at about 3200F. Of course, I did not get real close either. My mama didn't raise me to be a cinder. The danger was when they tapped the furnace into the teeming ladle and you get a fireworks show.
I have worn cotton-poly shirts at the forge for many years and while I had a few tiny holes, I never had a meltdown. I do wear a leather half-apron too.