explained in detail below preferably however the base 105 becomes more visible through the lens 101 when the device 100 has expired in order to enhance the visibility of the base 105 through the lens 101 when the device 100 has expired the base 105 is preferably brightly colored and or has indicia printed thereon such that the bright color and or the indicia are visible through the lens 101 when the device is expired referring now to fig2 in accordance with a preferred embodiment of the invention a timing device 200 comprises a lens 201 a base 211 and an optical medium 204 as described above the optical medium 204 preferably comprises a fluid layer 207 the fluid layer 207 can be comprised of any number of fluid materials but preferably comprises a transparent gel material which is either acid or basic and which is either conductive or insulating depending on the application at hand the optical medium 204 also preferably comprises an opaque layer 205 also referred to herein as a lens coating layer which does not imply that the opaque layer 205 is necessarily coated directly on the lens 201 the lens coating 205 is preferably formed from a material which will react with the fluid layer 207 when the device 200 is activated for example the lens coating layer 205 is formed from a hardened gel such as gelatin and thiosulfate preferably.