Charles Rennie Mackintosh is most famous for his rose motifs, but he also used triangles widely in his work, particularly at Derngate in Northampton, at Scotland Street School (where I first came across his use of triangles, the wonderful vivid green ones in the stained glass windows), and in his textile designs.
Here's how I carved a set of eraser stamps based on Charles Rennie Mackintosh's triangle designs:
1. Measure and mark the position of the triangles on your eraser.
2. Cut the triangle shapes out using a craft knife.
3. Draw any designs you want within the triangle shapes. I left some plain, cut one as an outline triangle, one in a chequerboard design (inspired by one of Mackintosh's textile designs), and one with stripes (inspired by Derngate).
4. Carve out the designs - I used Japanese woodblock carving tools, but you could use lino cutters or a craft knife.
5. Make use of the scraps by cutting them into other shapes to complement the triangles - for example I cut some smaller triangles, a small square, and a strip of mini triangles that could be used as a border, and everything came from one medium sized eraser.
6. Test your stamps and if necessary remove any excess areas.
Fun fact - this black ink pad is the first I bought, it's probably over 20 years old and still going strong even though it's my most used ink pad! And I bought it at the same time as two Charles Rennie Mackintosh rose stamps!
I did some test prints with the stamps, inspired by Scotland Street School and Derngate, then I stamped a sheet of paper all over, inspired by this textile design.