Emulsion - Coating the Screen

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If any product does the bulk of the work in printmaking it's photosensitive emulsion.  It's a plasticized coating that is applied in a wet state and allowed to dry on the screen.  When it's exposed an intense light source, the exposed areas will wash out of the mesh of the screen.  Where it has not been exposed to light, will stick tight to the mesh, providing a mask to block ink from flowing through the screen and onto the work.  Of course, like most things in printmaking, it arrives in a bucket.  To use it, the emulsion will need to be applied in a thin, even layer to the screen mesh.

After this has been applied and dried you have , essentially, a type of unexposed photographic film.  Like photographic film you'll need to work in a light protected area.  The lamps in this section of the print lab are safe for unexposed emulsion and a nice feature.

What if you want to screen print at home and don't have a dedicated light safe room?  Use common yellow bug-lights from the home center.  As long as other light sources are blocked out the emulsion will behave as expected!

Emulsion Types-


There are several types of emulsions available.  Usually these fall along the lines of a two-part emulsion or a pre-mixed one.  Of all the options, I would choose the longest shelf life and learn it's characteristics.  Some two-part emulsions may be forgiving as far as exposure time variability but can work out to be more expensive if it can't be used within the shelf life window.



Emulsions also are offered on one-coat and two-coat varieties.  With any chemically based material, read the labels and get familiar with what you're using.


Application-


To spread the emulsion, regardless of type, a scoop coater is employed.




The scoop coater is simply an aluminum extrusion wide enough to span the screen from side to side so the emulsion can be applied in one pass.  It has two edges, a narrow edge and a wide edge.  The thickness of the emulsion regulates the thickness of ink deposited on the media.  Use the narrow edge against the screen for most applications.  The wide edge can be used if a thick layer of emulsion is needed, for example when printing on heat transfer paper.  The thin side is good for about 90% of the time.  Also take care not to damage the edge.  Nicks in the scoop coater's edge will leave streaks of emulsion on the screen and can impact print quality in the end.


The wide, round edge on a scoop coater.





Opposite the wide edge there is a narrow one. Use this side against the screen.



Load the coater with enough emulsion to do the job,  about 1" deep in the bottom of the trough.  The application of emulsion is hard to explain but easy to do.  Starting on bottom, tip the coater so the emulsion runs forward and contacts the screen all the way across.  Then, in a even motion, move the coater from bottom to top, keeping a bead of emulsion against the screen at all times.  When at the top, pause and rock the coater back, keeping contact with the screen. Allow the emulsion to flow away from the screen and continue the last inch up the screen with the coater rocked back and lift it off.  There should be an even coat of emulsion, bottom to top!






Drying can be done naturally or in a forced air, dedicated dryer.  Both give the same result but the dryer is, of course, faster.  In the photo below, the screen dryer is the lower unit.  The upper unit is an exposure table and is covered in another post.


Coated screens can be stored in a dark cabinet for several months before use so, coat them in batches if you have the space to store them!  Most projects will consume several screens.  It's nice, but not completely necessary, to have all your color separations prepared in advance of a print run.




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