The first attempt was a fail, so I tried again! This time I made sure to wash the paper down properly.
The outcome was far more successful, the letters stood out and didn't fade as much after the washing process. I have not worked with cyanotype that much but I was pleased with this end result. The slight shadow cast by the clay/plaster added an unexpected detail to the work.
I would play with this process again, I want to explore cyanotypes over time to create layers of text.