Design the political image. Create this image in two sizes: one image that will fit inside the dimensions of a postcard -- 3.5 inches by 5 inches; the second image to fit on an A4 page.
Print or draw the two images onto separate pieces of A4 size acetate. The smaller postcard image should be drawn or printed in the center of the A4 page. Mark around the edge of the smaller postcard image.
Cut out the bits of the political image that you want to print on each acetate sheet. Place a thick piece of cardboard underneath where you are cutting to protect the work surface. This creates your poster and postcard stencils.
Place a piece of A4 paper on your work surface. Put the larger poster stencil directly on top. Line up the edges of the paper and the stencil.
Place the screen directly on top of the stencil. Mask off any areas or gaps on the underside of the screen that are not covered by the acetate stencil.
Place a blob on ink on the top of the printing screen. Pull the ink down the screen with a squeegee held at a 45-degree angle.
Pull up the printing screen from left to right to reveal your printed poster.
Repeat Steps 4 through 7 to print as many posters as desired. You will not need to add more ink to the screen unless you are doing a large run of posters. When you can't pull the ink down the screen anymore, add another blob of ink to the frame. Pull the poster stencil away from the bottom of the screen once you have finished printing posters.
Place a postcard on your work surface, blank side facing up. Place the acetate stencil with the smaller image on top of the blank side of the postcard. Line up the edge of the postcard with the edge drawn around your postcard stencil image.
Repeat Steps 5 though 7 to print the first postcard. As with the poster image, you can repeat these steps to create multiple political postcards.