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I'm relatively new to Blender (2 weeks in), and I'm working on Blender 2.81. Every time I edit my material it spreads out to the other objects as well. I am super confused, because the other objects are on different scenes and should react individually when materials are applied. I attached a photo below, and as seen, the pink color as an example spreads all over the place instead of the specific object. Any ideas? Let me know if I need to supply anything more.

enter image description here

As seen here, I'm trying to color the roof, but it colors everything else.

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    $\begingroup$ Objects can share materials. All of the other objects are using the same material, blender will not assign a new material to new objects you have to do it yourself. So create new materials and assign them to the objects you want. $\endgroup$
    – susu
    Jul 6, 2020 at 2:47
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    $\begingroup$ You are probably using the same material for all of the object. I'm seeing a number 8 on the right of your "Material" Name, that means that material is being used by 8 objects. Probably that's the thing if, so, you just need to click on that number (make you are in Object Mode) and you will be able to change that color only. $\endgroup$
    – Emir
    Jul 6, 2020 at 2:48
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    $\begingroup$ This is where a naming convention is handy. Rename this material Rooftop. Any object that uses the Rooftop material and has faces assigned to it, will in part be pink. See the docs docs.blender.org/manual/en/latest/render/materials/… Notice materials can be mesh linked (every object using that mesh has the materials) or object linked (setup material slots on a per object basis). $\endgroup$
    – batFINGER
    Jul 6, 2020 at 6:22

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The comments give the right answer (sorry to "steal" it, but otherwise they won't be marked as an answer). If you want an object to be the only user of a material you've given to multiple objects, click on the number next to the name. By default, the material called "Material" in your example will then be duplicated and renamed to "Material.001" and the active object will be the only user. Of course you can now assign this material to other objects as well if you want them to have the same material.

The advantage of having the same material on multiple objects is of course to be able to change materials, textures etc. on many different objects without having to merge them into a single object.

The advantage of duplicating a material by clicking on the number is, especially if you have a very complex node setup, that you can easily assign a material on one object that is similar to a different object and only make slight changes.

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    $\begingroup$ This is not entirely correct. Commented on question before seeing answer. blender.stackexchange.com/questions/185371/… Doing as above will also change the material on all objects sharing the same mesh, (eg created via Alt-D dupe linked) when the materials are mesh linked (the default case). Important to note that materials come from a global pool, same name means same material. Btw Don't worry about stealing answers from comments. $\endgroup$
    – batFINGER
    Jul 6, 2020 at 6:42
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    $\begingroup$ Of course you're right. I was just looking at the screenshot and since the objects have completely different shapes I was assuming they have different meshes. And when I was talking of "different objects with the same material" I was implying that they are not identical or linked. $\endgroup$ Jul 6, 2020 at 7:16
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    $\begingroup$ Agree. Decided in end to add an answer to elaborate and expand a bit on comment, in way of explaining how if some objects do share a mesh making slot a single user material will alter more than just the active object once again, also the choice of material link. May fall on deaf ears, but still IMO worth explaining for those that come to question where shared mesh is the case. $\endgroup$
    – batFINGER
    Jul 6, 2020 at 13:35
  • $\begingroup$ Good addition, it may definitely help someone who ends up here. $\endgroup$ Jul 6, 2020 at 13:43
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Material Assignment

Given your newness to blender decided to add this answer to explain another way you may encounter similar behaviour in the future.

Firstly highly recommend reading the documentation on material assignment

Materials are stored in a global pool in the blend file. A material with the same name, is the same material, regardless of mesh, object or scene.

Get into habit of naming materials on creation, eg in this case "Rooftop". If it is copied via pressing the users number to "Make Single User" its name will be "Rooftop.001". Beware will get as confusing as hell if you get to "Material.033" but only have 7 unique materials

All faces of meshes by default use material in the top slot. Other materials need to be assigned to faces. The default for a new object is often material "Material" in top slot. If none of your objects share a mesh the quick fix is well explained via @GordonBrinkmann's answer ie assign the mesh a new material for slot.

If in the future it is possible you may have objects that share a mesh, read on

Object and Mesh Linked materials.

Example with 5 cube objects, each using one of two cube meshes and one pink material.

enter image description here

Example, default cube "Cube" with pink "Material" mesh linked.

"Cube.001" is a mesh linked duplicate AltD, shares the mesh "Cube" shares the material

"Cube.002" Has a duped mesh ShiftD has a mesh copy "Cube.001" using "Material"

"Cube.004" and "Cube.003" are linked and unlinked dupes (with meshes "Cube" and "Cube.001" respectively) both with object linked material to "Material"

The material in top slot of object "Cube" is made a single user and changed to Blue.

Some observations.

The number you see next to a material is its users. For a mesh linked material this is the mesh, for an object linked material this is the object.

The users of the material "Material" originally shows as 4 despite 5 objects using it. This is because first two objects have mesh linked materials to mesh "Cube" counting as one user. The mesh "Cube.001" is another and the two object linked materials the other two.

In the outliner the mesh linked materials show up as children of the mesh (should have expanded one), the object linked materials as children of the object.

Making the material a single user on original cube => "Material.001" (Blue) is also changing the material on objects that share the mesh eg "Cube.001" object shares "Cube" mesh, since their materials are mesh linked. We have made the material in slot 1 of mesh "Cube", "Material.001".

Object "Cube.003" also uses mesh "Cube" but with an object linked material, it still points to pink "Material" as does the other.

Summary

Using a mix of mesh and object linked materials allows for example a default set of materials on a mesh (mesh linked) to be "changed up" on an object that shares the mesh, on a per object per material slot basis.

IMO it is good practice to have as few meshes and materials in a blend as possible. Learned this the hard way , my early blender files would be a mess of copied materials, meshes, armatures. Have written numerous scripts to try and clean it up .. post mess, the more organized from the start the easier it gets.. trust me

Hope this will in some way help when you get to adding common ubiquitous objects to scene , eg fence posts: can have a million fence post objects all sharing a singular fence post mesh, all using the same mesh linked materials.

To have one fence post red, object link and assign the material of one fence post object.... otherwise making material a single user will alter all fence posts to same colour, somewhat similarly to hassle in question.

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Just to answer in a single sentence:

Editing one material will affect all of the faces that have been assigned to use said material.

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