Another accident that came from experimenting with Draconian's metal tutorials. You will need G'MIC.http://gmic.sourceforge.net/
Set your FG and BG colours to dark and light grey ang use your gradient fiil tool to create a gradient making sure the gradient is set to FG to BG.
Create a new layer and open Filters>render>clouds>solid noise. Use the values below and press New Seed until you have something fairly light.
Put the layer into Grain Merge mode and merge down.
Duplicate the layer and run G'MIC>Colours>Metallic Look, adjusting the smoothness to produce a little banding.
Reduce the opacity and merge down.
Open Colours>colourize and get the colour you want. I used these values.
Make any final adjustments and do what you want to with the wood.