Chapter 10
Washing Out The Stencil After Exposure
Directly after exposure, quickly take your screen to your washout booth and immediately wet both sides. Once the screen is wet it is relatively safe in regular light. Wet, uncured emulsion will be less reactive to light at this point. Gently rinse the screen on both sides with standard garden hose pressure from a hand trigger spray nozzle. Be very gentle on the ink well side. This side can be slightly under cured especially with industrial black lamp exposure units and may look different in color or appear slimy or sudsy. Some degree of this is normal but it could also indicate an under exposure. After gently wetting both sides of the screen for about a minute, turn the screen so that the substrate side faces you and continue to gently rinse the stencil area. Now focus on spraying the water directly at and through the image areas of your design.
VIDEO: Exposing & Washing Out The Stencil
As soon as you wet the screen you should see the "latent" image of your design begin to emerge in the emulsion. Do not force it, be gentle. The emulsion should start to look lighter and thinner, eventually washing out. You should be able to see this happen and watch closely as you only want to spend the amount of time washing the screen out as is necessary to get the uncured emulsion out of the mesh. Once you can see that your entire stencil area is free of uncured emulsion, go to a wide, sheeting spray action with the water. Rinse both sides with a flooding, sheeting action running down the screen. This will help remove any scum left behind from the slightly under cured emulsion on the ink well side that you may experience with an industrial black lamp UV exposure unit. These are the types with the fluorescent UV bulbs. Never use paper or newsprint to dry a washed out screen. Allow the screen to dry by itself.
Allow the screen to dry and then do a post exposure if you are using a photopolymer emulsion. This will help the emulsion harden and be durable for longer print runs. It can also prevent the creation of pinholes during a print run. It is important to note that dual cure emulsions do not post cure. What is a post cure? You are simply going to take the exposed screen with the stencil washed out and dried and bring it back to the exposure unit. Then you expose it for the same time you did the exposure for on both sides without any film positives. Since you already made the stencil, the film positive is not needed for this part. More about post exposure and the video link is included in the checking for pinholes section for your convenience.
VIDEO: How To Post Expose An Emulsion Stencil
After the post exposure you will want to look for any clear soap scum like clogs in the mesh. You can hold the screen at an angle toward a room light and look for a colorful glare you would see from a soap bubble in the stencil area. If you see this clear substance reflecting a pearl like array of colors, then you have under exposed emulsion scum in the stencil. You must clear this out before going to press. It will not print and once it gets inked up, it will be nearly impossible to remove even with screen opener. Take a wet paper towel and wipe down the affected area in the stencil on both sides of the screen well. Then you can use an air compressor with very low pressure at about 24 PSI to blow out the moisture left over in the stencil. This will remove the emulsion scum and once dry, the screen will be ready for press.
VIDEO: Clearing Out The Stencil After Screen Washout
VIDEO: Screen Printing Production Tips: Washing Out The Stencil
VIDEO: Should You Use A Pressure Washer To Washout The Stencil?
VIDEO: Tips On Washing Out Screens