A material includes such properties as a main colour (‘diffuse’), the colour of reflections (‘specularity’), opacity (alpha). Opacity is the opposite of transparency, so a material with an alpha of 1 is completely opaque and not transparent at all whereas a material with an alpha of 0 is completely transparent. Materials can also include textures, such as a pattern of bricks or a wood grain texture.

The materials panel is in my opinion poorly designed for it is not at all obvious how to create materials and assign them to objects or faces. In fact you should think in terms of faces rather than objects for it is possible for different faces of the same object to have different materials assigned to them. The most important thing to understand is that you will be making a number of materials that will always be available to every face of every object. When you change a material the changes will affect every face of every object that uses that material.

To work with materials, first open the materials panel .

If the materials panel shows only this:  it does not necessarily mean that there are no materials in your project, it means that the selected object has no ‘slots’ for materials (I will call the empty panel in this image the ‘slots window’). To see what materials exist in your project click the Browse ID Data button  . You may see no materials listed, or you may see several. If there are not yet any materials in your project then create one by clicking ‘New’, otherwise just choose a material from the list. Either way, you will notice that not only do several new panels appear in the materials panel but also a ‘slot’ is created in the slots window, bearing the name of the material associated with the slot.

To make a new material, first click the Add New Material button  (the plus sign next to the X, not the other plus sign). It is a good idea to rename each material that you create. You can assign materials to faces either in object mode or in edit mode, but it’s probably easier to understand what is going on in edit mode. Select an object in object mode and then switch to edit mode - all the faces of that object should be selected. If you have several objects selected when you try to work with the materials panel then only the active object (the last one you selected, which appears surrounded by a lighter orange outline) will be affected.

In the materials panel is this area that I will call the slots window:

My image shows three slots which each contain a material (renamed yellow, red and blue) that can be assigned to selected faces by clicking the Assign button (Blender implies that materials are applied to vertices but in fact they are applied to faces, so you should be in face select mode  when you want to select faces to assign to a slot. In the above image the third slot containing a material called ‘blue’ is selected so if I were to click the Assign button this is the material that would be applied to selected faces. The slots window may contain any number of slots, or none at all. The materials displayed here will be a subset of the materials included in your project. For example, you might have created twenty materials in your project and the slots window of the currently selected object might contain three slots and thus three of the twenty materials. It is possible that different slots of the same object might contain the same material like this:  

This would mean that one set of faces has been assigned the material ‘yellow’ that a second set of faces has been assigned the material ‘blue’ and that other faces have also been assigned the materials ‘blue’. The contents of a slot can be changed to any of the materials existing within the project by clicking the ‘Browse ID data’ button  which will cause the full list of available materials to be displayed so that you can choose a material to occupy the selected slots. You can add a new slot by clicking the ‘+’ sign that is above the ‘-’ sign (the new slot will initially contain the same material that was selected just before you created the new slot, but you can change this to any available material by clicking the Browse ID data button as just explained). You can also remove a slot by clicking the ‘-’ button. If this slot corresponds to any faces in the selected object then they will no longer have a material assigned to them so they will become black. If you click the ‘X’ button then the selected slot will still exist but will not have any material associated with it – the set of faces that correspond to this slot will become gray.

As previously mentioned, when you change a material the changes will affect every face of every object that uses that material. If more than one object is using a material then when that material is selected a number appears next to it like this: . If you want to change this material for the selected object without changing it for other objects then click this number – this will in fact make a copy of the selected material with a new and unique name 

As previously mentioned, it is possible to work with materials in both edit mode and object mode. What happens if you work with materials while in object mode? You can do some of the same things you can do in edit mode – you can add and remove slots and you can change what material is associated with each slot (and thus with the group of faces that are assigned to that slot) but you cannot change what faces are assigned to what slot.

MATERIALS SUMMARY

Materials are best worked with in Edit mode. A full list of all the materials in your project can be dropped down by hitting the Browse ID Data button . To apply material to a selected object there must be slots in the slots window. Each slot is associated with a group of faces and each slot has a material associated with it. For example your project might contain twenty materials and a certain object might have four slots, each with a different material assigned to it and each associated with a certain group of faces within the object.

To apply a certain material to a certain group of faces in an object:

1. Select the object

2. Go to Edit mode

3. Open the material panel

4. If the desired material does not already exist in your object then create it

5. Create a slot in the slots window that will correspond to the set of faces and to the desired material.

6. Assign the correct material to the slot if it is not already assigned.

7. In Face Select mode, select the faces that are to be associated with the selected slot and click the Assign button.