Kudos on your efforts. Yet the experiment must be redone without dyes. The resulting stones must be handled in the same fashion as when done with dyes. If red colouring was found only after leaving the stones out in the sun, then a non-dyed stone must be left out in the sun as well, for the same amount of time, in the same temperature, same season, etc. Heat does produce chemical reactions. Have you had the outputted red colouring analyzed? The conclusions are far too premature.