The "Front" side of the slide is the EMULSION side.

There are always exceptions to rules but for the most part, all you have to do is pick the side with the most text on it either as the processor Logo such as Kodak or Fotomat or similar. Sometimes with plastic slides they will even have an imprint that says "This side towards the screen". It is surprising how many people miss this when it is so obvious. We have seen instances where the processor put the film in the slide holder backwards but these were processed outside of the USA. We have also run into instances where people developed their own film and the put them into plastic slide holders backwards.

Any text that you see when looking through the front of the slide, should be backwards.