The Union Jack, also known as the Union Flag, is the national flag of the United Kingdom. It symbolically joins the flags of England and Scotland by layering the red cross of St. George over the white cross of St. Andrew (which were featured on each independent country's flag respectively). Painting the flag is just a matter of constructing straight lines. The secret to painting your own Union Jack is as simple as painters tape.
Turn your canvas so that it is horizontally longer than it is vertically tall. Carefully study the Union Jack flag. Measure each section to calculate the ratio of length of each section in the flag. Use a ruler to measure each coloured section of the flag in inches or centimetres. Draw a loose sketch of the flag, marking your measurements as you go. The ratio of each sections side will be the same as you convert it to a larger or smaller size for your painting. For example, the bottom of the left blue section of the flag may measure 4:3:1 in inches. This ratio will hold true as you convert it to any size.
Use your painter's tape to mark out the white space on the Union Jack flag. It may be helpful to cut the thinner pieces of tape with an Exacto knife. Use a ruler to measure each piece of tape. This step is crucial to create symmetry in your Union Jack.
Paint red and blue in the empty areas after taping out the white space of the Union Jack flag. Copy the patterns of the flag. Keep a picture of the flag near to use as reference.
Pull the painter's tape strips away from the canvas to reveal the white space of the Union Jack flag. Allow the paint to dry.