How long does emulsion last before it expires?

This question is not a general one but one that also concerns emulsion chemistry. Because of this, I reached out to Ben Petsy and Ross Balfour at Saati to confirm some long-held understandings I had about emulsions. I was not disappointed.

As a general statement, when unopened, photopolymer emulsions (which include SBQs) will last a good couple of years when kept in stable temperature conditions. These conditions fall between the mid-60s to upper-70s for a temperature range. One of the things that can happen over time, especially with high solids emulsions, is they can settle. If the emulsion sits and is not agitated, you will want to vigorously stir it all up and let the air settle out before using. Another is the slight possibility of the growth of mildew in the container. While all of Saati’s emulsions come with a fungicide included, not all emulsions do. So, pay attention when opening the emulsion for any odd smells or patches of fuzz.

As for dual-cure or two-part emulsions, they have an unopened shelf life similar to that of the photopolymers. Once it’s opened and you add the Diazo, you have about six weeks before the emulsion goes bad. But here is where things get complicated. The shelf life is contingent on the temperature of the room, or in other words, the temperature of the emulsion. The hotter it is, the faster the diazo will go bad. The cooler it is, the longer it will last. These contingencies are due to the volatile nature of the diazo. It begins to break down the moment you put it in your emulsion. Higher temperatures speed up that process.

So, let’s say you are in Texas. It’s the height of summer, 100 degrees F outside, and you are not in an air-conditioned shop. Every room is at least 98 degrees F or more. Once you sensitize emulsion at that temperature, you have a three-day shelf life. Conversely, if you were to keep the emulsion below 40-50 degrees F, you can extend out to double the standard shelf life of six weeks.

—Ryonet