The next steps are optional and at your own risk, but I find the payoffs to be worth the effort.

Again lay the secondary mirror face down on a tissue. Use the flattest black spray paint that you can find. Holding the can at a high angle, spray once all around the secondary. This should cover the aluminized sides of the mirror and the silicon, preventing unwanted reflections and diffractions. Do not over spray, this will cause the mirror to stick to the tissue on the sides. Rather wait till it is dry and do a second coat.