I think that the products based on zinc sulphide without radioisotope activation will not and I think many products fall into this category. The key here is how long does it glow and will it glow all night? With this particular clock there is a healthy eighth of an inch clearance. A very important factor is the free space vertically between the two hands.We are going to apply a pad of 'glow in the dark' powder to them and the hour hand must then not foul the minute hand above as it rotates. Importantly for this project the hands are out in the open and can be worked on without removal from the clock mechanism albeit they are rather ornate but widely sold. It is a wall clock and quite large at twelve inches diameter which means that it can be easily read from fifteen feet away. Our chosen clock, rather a compromise, can be seen in the picture above. In our case, the project was for bedroom use so silence in operation was vital-this can be the source of some anguish as in our case where one partner can hear a pin drop at three floors down. For reasons that will become apparent simple chunky hands that have a large surface area will make the job much simpler. The clock should be reasonably cheap so that any disaster is not too disastrous. This is not easy to tell when the clock is on display in a shop and the information may not be easy to ascertain. There are many many clocks out there! We need to be able to access the hands so if they are behind a glass then we need to know for certain that we can get behind it to work. Please take a look at a previous 'ible here where some of the techniques used in this article were worked up. This article shown how they can be applied in situ with cheap nail varnish which is cellulose nitrate dissolved in an acetone/amyl acetate solvent and is very similar to the 'dope' used by model aircraft enthusiasts many years ago. The powders can be difficult to apply mainly due to their coarse nature which means that you cannot make useable paints from them and grinding impairs the light emitting property. The 'glow in the dark' powder far outperforms the old style zinc sulphide but the green light emitted is very similar. These powders are available in a number of colours but the green one has the best staying power and will emit light for twenty four hours after activation by natural or artificial light. We have come a long way from the days when zinc sulphide activated with radioisotopes such as radium or tritium gave good service-absolutely forbidden now! However it is now possible to obtain 'glow in the dark' powders based on rare earth doped strontium aluminate which do not need radioactivity. The luminous paint used on modern clocks tends to be disappointing and most will not last for a full night. ![]() It had to be effortlessly readable from the bed and the luminosity had to last through the night. We wanted a bedroom wall clock with luminous hands and display of five minute and quarter hour intervals.
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