How do you undo a join in Blender?

Unjoining objects in Blender depends on how they were joined in the first place. There are a few common scenarios, and each requires a slightly different approach. The most common solution involves separating by loose parts or by material.

Here's a breakdown of how to "undo" a join in different situations:

Scenario 1: Objects joined into a single object (Mesh)

This is the most common "join" scenario in Blender, where multiple objects have been combined into a single mesh object using Ctrl+J. To separate them again:

1. Enter Edit Mode: Select the object in Object Mode and press Tab to switch to Edit Mode.

2. Separate by Loose Parts (Recommended): Press P to open the Separate menu. Choose "By Loose Parts". This separates the mesh into individual, disconnected parts based on existing separations in the geometry. This works best when the original objects weren't directly connected by faces, but rather were just separate pieces of geometry within the same object.

   • Explanation: "By Loose Parts" looks for areas in the mesh that are not connected by any faces or edges and separates them into individual objects.

3. Separate by Material: Press P and select the "By Material" option from the menu. Blender will automatically separate the object into different parts based on the materials assigned to different sections of the mesh. This is useful if the original objects had different materials.

   • Explanation: If the original objects had unique materials assigned before the join, this is an effective way to separate them back out. Blender uses the material boundaries to determine where to split the mesh.

4. Separate by Selection: In Edit Mode, use selection tools (vertex, edge, or face select) to select the geometry you want to separate into a new object. Then press P and select "By Selection".

   • Explanation: This method gives you the most control, allowing you to manually define which parts of the mesh become separate objects.

5. Exit Edit Mode: Press Tab to return to Object Mode. You will now have multiple separate objects.

Scenario 2: Objects parented to one another

If objects are "joined" by parenting (one object is the parent, and the others are children), you need to unparent them.

1. Select Child Objects: Select the object(s) that are parented (the "children").
2. Unparent: Press Alt+P to open the Clear Parent menu. Choose "Clear and Keep Transformation". This will remove the parenting relationship while keeping the child objects in their current world-space location.

Scenario 3: Objects linked via constraints

Objects might appear joined because one object's movement is constrained to another.

1. Select the Constrained Object: Select the object that is being affected by the constraint (usually the object that appears to be "following" another).
2. Go to the Constraints Tab: In the Properties panel, find the "Constraints" tab (it looks like a chain).
3. Delete the Constraint: Select the constraint you want to remove and click the "X" button next to it to delete it.

Additional Tips

• Undo Immediately: If you accidentally joined objects, the fastest solution is often to simply press Ctrl+Z (Undo) immediately after joining them.
• Save Before Major Changes: It's always a good idea to save your Blender file before performing operations like joining or separating objects, so you can easily revert if something goes wrong.

By understanding the different ways objects can be joined in Blender, you can efficiently "undo" the process and restore your scene to its desired state.