We recommend to use the accessory – it will give the best results.
Otherwise, use a black surface. One of the ways to test for a good background material, is to scan it with SCiO and make sure no signal is received (reflection should be less than 1%, with no sharp peaks).
Using a CD is not advisable since it breaks the light into its components and sends each “color” in a different angle, some of it may be sensed by SCiO and disrupt the signal.