A triptych is simply an artwork that is spread across three panels. A triptych can use one image that spreads across three panels, or can be similar in theme, but use different images, or any combination of these. They are intended to be displayed side by side, and sold or used as one art piece. Triptychs can be made using almost any medium, but it is often done with painting.
Prepare canvas with 2 or 3 layers of gesso and your wide brush. Let each layer dry before applying the next layer. Wood can be used unprimed unless you are using oil paints. Prime any surface before using oils to preserve it. Prepare all of your panels at the same time. When the canvasses are dry and ready to be used, it's time to start the painting process.
Choose a palette (color choices and combinations) for the entire piece (three panels). Some variation is okay and interesting, but the colors should not be too different from each other if they are going to hang next to each other.
Start with an underpainting of any color you'd like, just to take away from the overpowering white of the gesso. Whether you are painting abstractly or painting a realistic image, keep sight of the whole picture instead of focusing on one canvas at a time.
Work the same amount on each panel, and try to keep them close in their levels of completion. It can be helpful to hang them on the wall while working and be able to stand back from them to really see your progress.
Let the panels dry completely, and frame them, if you desire.
Oil paints and many solvents for oils and acrylics are very toxic. Please wear rubber gloves to keep the toxins off of your skin and always keep these products out of the reach of children. These products should not be poured down the drain; they are very toxic to the environment. To clean brushes, rinse in a small amount of odorless mineral spirits that can be stored in a airtight jar. OMS can be used many times, in fact until it evaporates.