"Window Screen Windows" are by far the windows that I like the best for Z-scale model structures. The mullions are fine; making a double sash is simple; and, best of all, you can set the windows fully open, closed, or anywhere between.
The first step in making these windows is the purchase of supplies and collecting your tools.
I bought the smallest roll of grey plastic window-screening material that I could find at Lowes. I expect to die before using it up.
For paints, I use whatever comes to hand. Most often this means using Model Master and regular Testors flat enamels. Always spray these outside or in a well-ventilated area while wearing a proper respirator mask. Liver damage is not to be fooled around with!
Because the screening curls, I generally tape 6" x 12" pieces down to heavy cardboard before spraying. I also cut up paper bags to catch the overspray.
Spray using a nice even stroke. I like to let the spray paint warmup in the sun or in some warm water. Warming the paint helps the paint atomize well. If you are painting a styrene surface, allowing it to warm in the sun also seems to help in getting a clean, even coat of paint. Important: Warm. Do not heat. Heat leads to explosions. Never use an open flame near spray paint.
Allow the paint to dry thoroughly before proceeding to the next step.
Once the paint has dried thoroughly, you are ready to bond the window screening to the clear styrene. I've been quite pleased with Krylon All Purpose Spray Adhesive (7010). I'm sure other spray adhesives would work. Make sure to test them on the window screening and the clear styrene. Some glues react badly with plastics.
Turn the painted window screening over and, in a well-ventilated area , lightly spray the back with adhesive.
Then gently drop the clear styrene onto the glued surface. Do your best to line it up to avoid wasting styrene, but you only get one shot. If you lift the styrene, it will become smeared by the glue.
Very gently smooth the styrene to make sure that you've got a good bond.
Allow the glue to dry overnight. Really. Wait. Once the glue has dried, you can use a small pair of scissors to cut out any size window that you'd like. You can also use a sharp knife, but I really like the control that a pair of sharp scissors gives me. By changing the orientation of the screen, you can get different widths and heighths because window screening is made up of little rectangles.
With a little thought, you can make all sorts of windows for your z-scale model structures.
Windows in a Z Scale model of a Sears Kit House from the 1920's.
Large industrial windows and small dormer windows in a scratch-built brick brewery.
Two different types of windows in Z-scale storefronts. By simply turning the screen material you can make either tall narrow windows or short broad windows.
By using different screen sizes, you could make windows for other scales. Plastic window screening is a great material to add to your bag of model building tricks.