Quote - I should have said screenshot of the material room while the material is selected. This shows all the nodes.

First the math function: Create a new node by right clicking on an empty space in the material roomm - select New node, math, then math functions. Now a new node is created. Click on the arrow in the node and you can select Subtract (or any other you need). You either put a value in value1 and value 2 or you can put another node in it. The left top of the node can connect to another node's input values - it will draw a line to show what is connected to what

Now what is needed: The scrawlings have to be seen and not be transparent. So we want to connect a texture which has black for the scrawlings and white or grey for the rest. If the texture is the other way around, you can connect the texture to the subtract node to create it. But you have a correct onel. So what you need to do is to connect the texture with the black for the scriblings to the refract value - this one is in the surface node directly below where the refract node is connected. Connect the texture to that value. Set the value to 1.

Now the texture controls what part of the table is transparent and which part is not (it controls the refract node)

If you have that - post a screenshot of how everything looks in the material room and a render. Then tell us what you want changed

 

 

Okay, here is the Material room for the top of the table:

 

And here's the Mat Room for the Under Surface of the table:

 

And here's the render:

 

What I'd like is the purple colour to be darker - less lilac and more purple.

The black designs are now looking correct - so with no colour in the top now - I'd need to adjust something in the under surface - yes? No?

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