http://conraddamon.com/pdga/2013/rules2013.html
801.02 Discs Used in Play
Discs used in play must meet all of the conditions set forth in the PDGA Technical Standards.
A disc which has been modified after production such that its original flight characteristics have been altered is illegal, excepting wear from usage during play and the moderate sanding of discs to smooth molding imperfections or scrapes. Discs excessively sanded or painted with a material of detectable thickness are illegal.
A disc which is cracked or perforated is illegal.
A disc that is questioned by another player or an official is illegal unless it is subsequently approved by the Director.