If you are a DIY printer, using the sun to expose your screens is an effective and free way to make your screens.
I would recommend using a dual cure emulsion (the type that requires Diazo to activate) because this kind of emulsion is more forgiving than pre-sensitised emulsions. I recommend this because it is a little more challenging to control the sun exposure, and you will want a bigger window of time for exposure.
The best time to use the sun for exposure is at noon, so you can get the most concentrated UV rays. Coat your screen and let it dry in a light-safe area. Once it is dry, place the film on top of the screen where you want your stencil to show up. It is ideal to place a piece of glass over your film so that when the sun exposure is happening, it keeps a positive contact with the screen. You don’t want the film curling up or moving from the screen or you will not have a clean stencil. Before you leave the light safe environment, make sure to cover up your screen so it does not expose before you are ready. You will see in this video that Ryan also leaves a piece of cardboard underneath the screen, this is to prevent any sunshine rays from bouncing around, causing an uneven exposure.
Check out this video and let Ryan show you step-by-step how to make your own sun exposure unit.