We knew that architectural drawing was going to be hard.
First we prepared paper with colours and stains as you can see below.... dirt, coffee, waterclour. But the purple and blue were made by the coloured berries below the picture. Some people also applied colour using flower petals from the garden.
Then when the paper was quite dry, we covered the sheet with charcoal
then we chose a subject and worked on rubbing the charcoal off again to create the white, and filling in with black compressed charcoal to achieve the darks - you can just see the colours of the preapared paper peeping through