How to coat your screen with Photo Emulsion
What is Photo Emulsion?
Diazo Photo Emulsion is liquid that has very tiny solid particles in it. It becomes sensitive to light when the diazo sensitizer is added to it.
During drying the liquid evaporates out leaving a solid coating. Once exposed this coating will create a solid barrier in some areas and wash away in others creating your image.
Getting a nice smooth even coat of photo emulsion on your screen is essential for getting a good exposure and durable stencil.
Having a well prepared screen and the right tools is essential.
If you have not degreased your screen yet read: Screen preparation for Photo Emulsion
Get some emulsion: Hunt the Moon Photo Emulsion
Coating the screen.
Generally we recommend two coats of emulsion on the printside and one on the squeegee side. (On higher mesh counts you can go to one coat each side to make lighter prints. More on that soon)
Fill your scoop coater just over half full. Too much it will spill out of the sides. Not enough and the coat will be patchy.
Make your screen secure, we have used a block of wood to push against. Its easier like this as you will have more control with the scoop coater. This prevents the screen slipping or moving and emulsion going everywhere. It allows better control of the scoop coater for a better finish.
Starting with the printside, place the scoop coater about an inch from the edge of the frame, (most printers will tape this gap up before printing anyway).
You cannot print edge to edge anyway so no need to coat it. (its also quite tricky to cover that space).
First coat on print side
Place the edge of the scoop coater against the mesh and tilt it forwards until the emulsion touches the mesh all the way along. Use the yellow edge of the scoop coater as a guide on what angle to use.
Pull the scoop coater up the screen. Use a smooth movement with even pressure. This will give an even thickness for your stencil. (You don't want a thick patch anywhere. It wont expose correctly and could lead to premature breakdown of your stencil)
Do one coat up the screen, making sure there are no bubbles on the surface. Go nice and slow. Stop about the same distance from the top of the frame. Turn the screen so you coat the next layer in the other direction staying on the same side.
Second coat going the other way up the screen
Do one coat on the squeegee side, matching the placement of emulsion to the printside. Once both sides are coated you can scrape off any excess with the scoop coater. Make sure to always do the squeegee side last.
Coating the squeegee side
Clean up any drips or excess at the edges of the screen.
Place your freshly coated screen in a dark, dust free place with the print side facing down (that's the flat mesh side). A cupboard or box is fine. Remember to raise the screen off the bottom of the box so that the emulsion does not touch anything.
This will let the emulsion sink to the print side for a better gasket to hold your ink in.
Coat today, use tomorrow is our recommendation.
Next Step: How to Expose your screen.