are utilized as explained below the invention provides techniques for manufacturing a thermochromic medium by treating a substrate with a thermochromic coating on both sides and applying heat to on one side of the medium such that the heat will not produce a visible marking on the other side of the medium the manufacturing techniques provide this functionality despite assuming that heat applied to one side of the medium will conduct through the substrate with a sufficient intensity to activate a thermochromic coating applied to the opposite side of the substrate fig2 a shows a visual representation of a technique for thermally marking a ballot on both sides according to the invention in this example the thermochromic medium is described as a ballot 500 based on a paper substrate however it will be readily apparent to those possessing ordinary skill in the art that any thermochromic medium may benefit from the technique in this technique a thermochromic coating is applied to selected regions on each side of the substrate in an exclusionary fashion according to these techniques no region of paper exists in which thermally sensitive coatings are applied to both sides of the paper on the front of the ballot 500 the sets of candidates running for several offices are press printed at left the boxes 531 for indicating a voter 39 s preference for a particular candidate are press printed in a vertical column at right the entire column of boxes is backed by a thermochromic coating 521 on the back of the ballot a series of services are press printed below a set of press printed instructions and a set of boxes 532 for indicating the voter 39 s perceived importance.