Usually Tom and I relay a story of our own mistakes, which folks seem to enjoy hearing about. Today it is a mix of my woes and someone else’s.
On a Facebook group this morning a fellow traveler in the world of screenprinting was having trouble with screens that would not wash out.
What can cause this?
Andy MacDougal mentioned expired emulsion as a possible cause. This is an issue that we have at Mirror Image recently. Read the expiration date on your emulsions and rotate them so you are using the oldest ones, not leaving the old one in the back of the shelf and using the newly purchased ones til the old one expires. Keep them in a cool place.
Diazo emulsions have approximately a one year shelf life if kept at room temperature and no direct sunlight. They will last longer if at a colder temperature. Don’t buy more than you need in a few months, and if you do keep it cold, but not freezing. Pure photopolymers will typically last 18 months or if kept very cool and dark, possibly for years, even if the manufacturer says one year.
Some emulsions have the date on them, some have a code. In the case of this KIWO emulsion, the last four numbers of the batch are the key, 1811 means 2018 in the 11th week. Check with your distributor if you are not sure of the date.
In this case the distributor Martin Supply put the date on the emulsion and this emulsion is out of date.
Besides figuring the age by the packaging, these are the signs of emulsion that has degraded by being old:
– the diazo has turned from light yellowish green to a dark color
– the smell will be more pungent, almost a vinegar smell
– you will have difficulty developing your images
– you will have trouble washing out the exposed image
– you will have difficulty reclaiming the screens
That all is for emulsion on the shelf.
If you have mixed it up, you will only get 4 to 6 weeks of pot life, longer if you refrigerate it.
This all also points to you having a trusted distributor you work with that won’t sell you old product and that will keep you informed about shelf life.
Shout out to Dave Dennings of KIWO for help in writing this.