First of all, I'm quite new to Blender and 3D graphics in general, so this problem might be trivial, but I can't seem to figure out what is going wrong here.
I decided to put a bump node on a metallic texture to simulate scratches. At first, I was getting "bumps", and also they were way too defined, so I ran the image through a math node set to -0.0005 which solved the problem and I was quite happy with the result (as you can see on the right side of the image).
But then I noticed that the texture was "inverted" on one side of the cylinder, thus showing "bumps" again, so now there are ridges on one side of the cylinder, but bumps on the other. Obviously, though, I want there to only be ridges on the whole object.
At first, I thought it might be caused by the negative value on the math node, but when I put in a positive value, the problem is identical but inverted (ridges are replaced with bumps and vice versa).
So my question is - why? What is causing this and how can I fix it?
The scene is lit with a single point light. Below I've included images of several views of the problem as well as the node setup I am using for the metallic texture.
Thanks for any help.