Control multi-material object transparency I'm animating the assembly of an equipment, I have a couple of materials repeated on multiple objects, and also some objects have multiple materials assigned (so there is a blue paint material, red paint material, shiny metal, etc., and some objects can have the three of them).

What I need is to control the transparency per object, in this case to animate a "fade in" for each piece of this machine. It would be impractical to duplicate every material and then synchronize the materials on the same object to fade in at the same rate.
there has been a recent change in blender, that lets you use a custom object property inside a material node tree. Here you have a tutorial to set it up.
https://youtu.be/WWwS-0AHotY
I faced the same problem several years ago, and the solution at that time was using node groups, but it was quite time consuming.