The half square triangle unit is probably the most commonly used patch in a quilt block -- well it is second only to the square. It is made simply with two triangles, filling up half the square each -- hence the name. Take a quick look through this website, or in any quilting magazine, and you will start to notice that this half square triangle, regardless of its size, is present in more quilts than not.
Free Quilt Block Pattern
Who has not heard of the Underground Railroad? Well if not, a brief history is that it was not a train at all, but a secret network of people who assisted slaves during the 19th century to escape from the southern states, staying in secret and hidden "safe houses" on the way. The slaves followed the north star to northern states and Canada where freedom awaited.
Is it any wonder that this nine patch quilt block called Underground Railroad would be a directional type of block featuring a definite path? Besides offering wonderful results as you place your blocks in your quilt, directional blocks are good choices to use as "connector blocks", used side by side with a different block which results in a secondary pattern emerging. (At some point, I hope to offer patterns for two block quilts, but that is still on my "to do" list.)
The sample quilts illustrated show how secondary patterns can emerge with just this one block, by using simple 90 degree rotations. What interesting arrangements can you come up with?