Making a collograph plate

It's a while since I last made a collograph printing plate, but after making the quick watercolour sketch of the trees a few days ago I decided that this might be the best way to realise it as a print.   So I'm underway!  I still have to make a decision about what looks like a railway tunnel on the sketch - it was actually a single arch of Archer's Hill Gate (there are three) which was partly hidden behind the trees.  When it was constructed in the 18C, there would have been few trees to get in the way but now is a different story.  I'm going to make a background layer too, so that I have some contrast of textures and colours and I'm hoping this will give a feeling of depth to the print.  Keep your fingers crossed for me.  It's a lot of work if it doesn't work!