There are mediums out there for just about every need. They’re all made of polymer resins exactly like acrylic paint, but they don’t contain pigments. As a result, you can add as much medium as you like to your colour. But remember: The more medium you add, the more you disperse the pigments.
Adding a medium to colour increases its volume and improves its transparency, apart from one or two brands that only increase volume. Although mediums come in medium and high-viscosity variations just like paints, they do not need to be used only with paints of a matching viscosity.
Do I have to mix mediums and paint of matching viscosity?
Be aware that if you mix a medium with a paint of a different viscosity, the medium may thin or thicken the consistency of your paint as a result. Medium-viscosity mediums have a consistency that’s similar to paint in jars.
Glossy medium is one of the most versatile acrylic mediums. When mixed into colours, it makes them more fluid and gives them a shiny finish. It’s milky when wet, but dries completely clear. In addition to giving added transparency to colours, it’s a very good choice for glazes. Like other acrylic products, glossy medium is water-resistant once dry, stays flexible and doesn’t yellow. It also makes an excellent binder for powder pigments to create medium-viscosity paint, and it can be used as a shiny varnish for dry paintings. Avoid re-working a medium that’s been applied and has partially dried; you may end up with white streaks that can’t be removed.
You can use glossy medium for image transfers. First, you need to apply quite a few thin coats to your image (20 or more) until a solid film is created. Then, soak the image in water for a few minutes, and gently scrape the paper fibres from the back. Let it dry, and use the same glossy medium as a glue to affix the image to the surface you are using for your project.
Glossy medium can also function as glue on a variety of surfaces, as a fixative for crayon or pastel (diluted half-and-half with distilled water and misted using a sprayer or airbrush,) or as a colourless base coat to replace gesso. For serigraphy, you can use it to make permanent water-resistant masks. Glossy medium can be used instead of Mod Podge when you’re covering objects with fine paper, and as a final varnish. It’s just as transparent, but more water-resistant than Mod Podge once dry.