Key for Coating
Coating a screen with a Diazo Photo Emulsion is a critical step in the screen printing process. It lays the foundation for transferring your designs onto various surfaces with precision and clarity. If you're new to Screen Printing or looking to refine your coating technique, this guide will walk you through the process step by step.
What is Photo Emulsion?
Photo Emulsion is a light-sensitive substance used in screen printing. It forms a stencil on the screen by hardening when exposed to light. Coating the screen with emulsion and exposing it creates a barrier that allows ink to pass through only in desired areas, enabling the transfer of designs onto surfaces.
Whether you purchase our 250ml or 1ltr Photo Emulsion Set, both will require you to mix the Photo Emulsion and Diazo Sensitiser, details on this can be found in the product description here.
Before we start, make sure you have degreased your screens, this will ensure you have the best screen possible for applying photo emulsion - read more here.
Before we begin; make sure you have all the necessary materials at hand. You'll need a Screen (wooden or aluminium works), pre-mixed Photo Emulsion, a Scoop Coater, a spatula or pallet knife, access to a darkroom/light-safe area and a flat surface for drying.
Let's Coat ✨
We prefer to apply two coats of emulsion on the print side and one on the squeegee (ink)side. This is how we coat screens for custom exposures. On higher mesh counts you can coat once on each side to make lighter prints. If you do this you will need to adjust your exposure times accordingly. (A thinner coat will expose faster).
One last tip: When it comes to applying the Photo Emulsion, we recommend you place the scoop coater at least an inch from the edge of the frame. You cannot print edge-to-edge anyway so no need to coat the whole screen to that extent - it's also quite tricky to cover that space. Most printers will cover this gap with screen tape. We use Blue Screen Tape
Step 1 - Secure the Screen
Secure your Screen, in this instance, we have used a block of wood to hold the screen against. It's easier like this as you will have more control with the scoop coater. This will also prevent the Screen from slipping or moving and the emulsion going everywhere.
Step 2 - Fill it up!
Fill your Scoop Coater to half full with the pre-mixed Photo Emulsion. If you pour too much, it will spill out of the sides. Not enough and the coat will be patchy. Going half full is the perfect balance.
Step 3 - Print Side
Starting with the print side, place the edge of the scoop coater against the mesh and tilt it forward until the emulsion touches the mesh all the way along. Use the plastic parts on the ends 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 to your stencil. (You don't want a thick patch anywhere. It won't 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.
Step 4 - Print Side
Now it's time for the second coat on the print side; turn the screen, using the same side so you coat the next layer in the other direction. Use the exact same coating speed and angle.
Step 5 - Squeegee Side
Now you'll want to flip the screen to the squeegee side. Do one coat on the squeegee side, matching the placement of the emulsion to the print side you just did. As a rule of thumb, the squeegee side only gets one coat. Make sure to always do the squeegee side last.
Step 6 - Remove any excess
It's that simple! You have just coated your Screen. Now we recommend once both sides are coated you scrape off any excess with the scoop coater. Also, clean up any drips or excess at the edges of the screen. You should now have a finished screen with a nice smooth even coating!
It's that simple ✨
And that's it! Good job. We recommend once you have coated the screen, you use it exposure the next day. A clean dust free area that is dark with no light source coming in is best. If you have a dehumidifier then use it. Humidity in the drying space needs to be 50% or less and not hotter than 30 Celcius.
Use airflow to help dry your screens, but don't be tempted to place a fan directly on the screen. This will just cover your screen with dust and dirt. Also, be sure to keep the edge of your scoop coater clean and free from dents or nicks, these dents and dry emulsion will make streaks on your screen.