So after deleting a material from the blend file, it left all objects that were using that material with this empty material, how do I remove it from every object?
Hi there!
Itās called a āmaterial slotā - even if you donāt have a material assigned to it, you still can assign faces.
To clear this, thereās a
- little arrow icon to the right of the material list. Open it and press āRemove Unused Slotsā (works only on active object)
OR - go to Object > Clean Up > Remove Unused Material Slots (works on multiple selected objects)
Doesnāt work, either way nothing happens
After it has been deleted you can try saving the file and reloading it. This seems to work for other things no longer connected to nodes and removed from assets.
Try looking in the āoutlinerā window click on the scenes dropdown and select āorphan dataā. There may be objects or materials that have a fake user or something that prevents them from being deleted
I have an old free script called Atom Bomb made by Grant Wilk that accomplishes this task, along with many other useful removal tools. Not sure if it still works, but may be worth a try. I wonāt post the script here since I would be stepping on the authorās toes, and I donāt remember where the download came from, but google might be able to help (I would search for āGrant Wilk Blenderā or some such, rather than āAtom Bombā 
)
None of this works, atom bomb got deleted by grant off blender market, saving and opening doesnt do anything, and orphan data doesnt have anything to do with that material, heres the blend file https://www.mediafire.com/file/w8bsyhd2lo4ag2r/achivement.blend/file
I donāt think you understood my problem
Did you try it?
I literally say in my first message that I delete the material from the blend file, and I need to delete the leftover material slot from all the objects
It has to be something specific to your systemā¦
either File > Clean up > recursive unused data Blocksā¦ or the way I showed permanently removes ALL unused materials and slotsā¦I have not been able to reproduce your errorā¦
The only other thing I can think of would be an appended instance might be the causeā¦but you didnāt say if they were instancesā¦ and at this point we are only guessingā¦
Nope sorry, tried that already, the leftover stays, I linked the blend file above
Good afternoon, @stefyan563! Welcome to the Blender Artists community! I downloaded your file and was able to reproduce the issue with the remove unused material slots operator not removing your empty material slots in Blender 4.0.2 on MacOS Apple Silicon. This may be either a regression on a newer version of Blender or there may be something wrong with your file itself. Of course, I was able to manually remove the empty material slot using the subtract button on the material panel, but it would be tedious to do that for all of your objects with an empty slot.
Interestingly, if you add a new empty material slot and then run the remove unused slots operator, it removes the newly added one, but the old empty slot remains. Iām digging into your file to see if I can compare the two slots (old empty slot and new empty slot) to see why the old empty slide is not being removed.
Its technically still used, blender just draws the default grey color
Soā¦This is a bit strange. I think Iāve found out your issue, and Iām still working out the best way to fix it, but Iām not there yet. Let me lay out what I think is going on. I believe the Blender built-in operations function with certain assumptions - without looking into the source code, Iām sure there are certain checks that are completed before operations begin like a short circuit to avoid starting something that never ends (endless loop). I believe that through my Googling, the assumptions that Blender makes are:
- One and only one material slot can be assigned to each face.
- The Remove Unused Slot and Remove Unused Material Slots operations only purge those material slots that arenāt assigned to any faces.
What has happened in your file is that somehow your objects have found a way to have multiple materials assigned to the same faces. What that means is that even though you ādelete/unlinkā your material from that objectās material slot, that āemptyā material is still technically assigned to faces on your object. The Remove Unused Slots operator looks within your material for slots that have zero faces assigned to them, and finding none, exits printing {āCANCELLEDā} to the terminal.
Weāve broken assumption #1 and #2, so how do we remove those empty slots? Well, hereās my thought. You can still use the bpy.ops.object.material_slot_remove() function on your empty slots, and they are removed (whether they are removed cleanly, I cannot say). So, we really need to loop over each selected object, see if it has a material slot that is named empty string āā, and run the material_slot_remove() function on it.
Iāll try to get something working in the Python Console and let you know what I find out.
Probably something to do with how Plumber imports maps, but thanks, Iāll be waiting
Good news! I got a script working to remove material slots that have the name empty string āā. I ran it on your supplied file, and it removed empty slots from 516 objects. After re-saving the file, the file size went down by almost 2MB.
Hereās your disclaimer - this may destroy your computer and/or the universe. Use at your own peril.
Iāve attached the .py file for you to download. Hereās how to use it:
- Download .py script.
- Open Blender.
- Switch to the Scripting workspace.
- Within the Text Editor, open the script.
- Hover your mouse cursor over the 3D Viewport and select all by pressing A.
- Press the Run Script button.
- ā¦
- Profit.
If anyone would like to review/critique my code, Iāve pasted it below. Iām sure I could have documented it better, but it is almost dinner time and I donāt know what Iām going to eat yet, so Iām going to go do that. Please let me know if you run into any issues or have any questions!
Hereās a video of it in progress:
Script:
RemoveUnusedSlots.py (796 Bytes)
import bpy
intCounter = 0
# Grab list of selected objects
lstSelectedObjects = bpy.context.selected_objects
# Loop over collection of selected objects
for Object in lstSelectedObjects:
# Set current object as active object
bpy.context.view_layer.objects.active = Object
# Find if there's a material index with the slot name of empty string '' and set it active
key = ''
try:
Object.active_material_index = Object.material_slots[''].slot_index
except KeyError:
print(f"{Object.name} doesn't contain an empty material slot. Continuing...")
continue
# Run the remove slot function on active slot
bpy.ops.object.material_slot_remove()
intCounter += 1
print(f"Empty slots removed from {intCounter} object(s).")
print("Script completed successfully.")