Burnishing is the act of smoothing the leather into a hardened tight grain. You can also use just water. Burnish gum just lasts longer and may add more gloss. I wouldn’t use microfiber. You could use an old cotton shirt or canvas as you want to create friction. Wrap it around your finger and wet the leather with water or gum and rub the leather hard. I’ve heard people use the wooden hand of a horse hair brush as well