Oops! You've accidentally bought one can of eggshell paint and one in semi-gloss. While you can't return paint that's been custom tinted to your specifications, you can mix paints together as long as they're each the same type, such as latex.
While the amount of sheen in a paint may vary from one brand to the next, they all follow a basic chart that ranges from flat to shiny. The least reflective are called flat; some brands also offer a matte finish, which is slightly shinier than the flat. Eggshell paint comes next, followed by satin, semi-gloss, then gloss or high-gloss. The shinier or more reflective the paint, the more durable it is, too. High gloss levels are excellent for areas that require frequent cleanings, such as door trim in a kitchen or bathroom area.
Keys to Mixing Success
While eggshell and semi-gloss paints are compatible for mixing purposes, poor choices could result in a paint that produces clumps or streaks when applied to the project surface. The best way to ensure the paints mix well together is to choose the same brand and the same type for each, such as latex enamel. Don't mix oil and latex; latex is a water-based paint, so mixing the two would be like trying to mix oil and water.
Sticking with one brand of paint is the best way to ensure that eggshell and semi-gloss will mix successfully since one brand may not have the same chemical structure as another and therefore may not be completely compatible. Even mixing paints within the same brand or product line may not result in success, so it's best to make a small test batch before mixing all the paint together.
Making a Test Batch
Mix a small batch of paint to ensure both paints are compatible with one another and to see what the end result will look like if using different shades. Start with one teaspoon of each paint in a disposable cup, stirring until the paint is a uniform color. Brush the paint onto a cardboard scrap, covering at least a couple inches so you can see how it really looks when dry. If you don't quite like the end result when blending colors, adjust the paint ratios and make another test batch. Write down the correct ratio and stick with it when mixing one large batch later.
How to Blend Paints
Open and stir each can of paint with separate paint paddles or stirrers until the paint in each can is a consistent color. Place a sheet of clean window-screen material over a five-gallon bucket, taping it securely over the sides of the bucket. Pour the desired amount of each paint through the screen to strain out chunks and clumps. While this isn't necessary with fresh paint, it's extremely useful when working with older paints that may have partially dried out. Once the paint flows through the screen, remove the screen and set it atop a tarp to dry. Stir the paints together with a paint-stirrer bit attached to a drill until there's no variation in color.