A key part of the screen printing process is the photo emulsion, when purchasing photo emulsion it good to note that it come unsensitized which means if you put it onto a screen it would be useless. Make sure that when you buy photo emulsion to check whether or not it comes with the sensitizer, in this case I have to buy the emulsion and the sensitizer separately.
You'll notice that when you open the emulsion up that it be a bright blue colour (below) this means that it hasn't had the sensitizer added. The sensitizer come in a small bottle (picture above on the right), the bottle will feel light and it will seem that there is nothing in there, DON'T PANIC the sensitizer comes in the form of a paste (normally a dark green colour) that you need to add liquid to.
For the sensitizer I used I had to fill the bottle 3/4 of the way full and give it a shake before adding it to the emulsion, this may not be the case with all sensitizer (though I think it is). Make sure you read the instructions on the side of the bottle just to make sure.
Once you have added the cold water to the bottle and given it a good shake you then need to add it to the emulsion.
Using a stick give the emulsion a good stir for a few minutes to make sure the sensitizer is fully mixed, you'll notice the emulsion will turn from blue to a green/turquoise colour as you mix it together.
Once it is fully mixed in it should resemble the colour below (colour may vary in shade depending on the brand of emulsion you use). If there is any blue left in the mixture just give it another quick stir until its all gone.
And your done!! it's as simple as that.
Remember that the photo emulsion is light sensitive so make sure the lid is on properly and store it in a cool dry place. Once you have added the sensitizer the emulsion will have a shelf life of about 3 - 3 1/2 months (the emulsion normally has a shelf life of about 1- 3years if left unsensitized).
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