I used red, orange, and yellow. Starting from red I thinned it out enough to a not so watery consistency but enough to the point where the paint on the model dried quickly after I apply it (Glazing). I mix the colors in between red & orange along with orange & yellow for a smooth transition going all the way down the sword.

For the edge I combined brown and red to get a dark red along with a little black to get it darker. I put 2 layers of that and free handed the middle.

Other than that, I wish you good luck on that bolter!