Hi again everyone 
I looked at the engraving example and it looks a bit hard for me right now, but I’m going to try the DiffuseDetailMap (Detail Diffuse Map?).
Right now I have my metal material with no main DiffuseMap, and UV1 with a decoration. So if I understand it well, I can put my logo on the blade with the DiffuseDetailMap on UV1?
I also searched for examples in other product customizers and I found this one that is interesting.
In this one, their logo blends with the decoration (leaving a border around the logo). They can rotate the texture, that makes me wonder if they first generate an image outside of their 3D engine, mixing the decoration and logo (in a html canvas perhaps?), and only then they put it as texture on their 3D model.
Is that a crazy and heavy processing idea? 
I already use something like that. An user can send his own picture, I load it in a canvas, change the pixels so it becomes transparent and greyscale, and set it as a DiffuseMap. It works OK as long as you send a PNG.
Some gifs !
The exemple configurator I found
My work so far (you can try it also here but it might not work 24/24 because I regulary break everything haha, and don’t mind the mess in the code, I should will clean it up)
