In this tutorial, I will show you how to make a procedural rusted metal material using the shader nodes in Blender for your project.
Warning Decal
I will first make a Normal Map for my warning decal
I open GIMP and make a new document that is 2048×2048 with a transparent background
I drag-and-drop my decal onto the document
I use the Scale tool to rescale the decal
I export the decal as a PNG
To make the Normal Map for the decal, I go to Filter > Map > Normal Map
I will use the default options
I then export the Normal Map as a PNG
Barrel Material
Make sure you have the Node Wrangler add-on activated under the Preferences
The barrel I am using is available for free if you want to follow along
I will use the auto-UVs provided by Blender since it is a good unwrap with little stretching
Under the Shading Workspace, I add a new material and name it
I select the Principled Shader and use CTRL + SHIFT + T to open the texture maps I downloaded for my material
I can now use the Mapping Node to change the scale of the textures
Decal Material
Now I want to add the decal to the barrel
I use SHIFT + A and add a Diffuse BSDF Node
I use SHIFT + A to add an Image Texture Node and open the decal image
I connect the Color output to the Color input of the Diffuse Node
I use SHIFT + D to duplicate the Image Texture Node and open the Normal Map
I change the Color Space to Non-Color
I connect the Color output to the Normal input of the Diffuse Node
I use SHIFT + A to add a Mix Shader Node between the Principled Shader and the Material Output Node
I connect the BSDF output of the Diffuse Node to the bottom input of the Mix Shader
I select the three Nodes for the decal and use CTRL + J to join them
I can then right-click and rename the Frame
I repeat this process for the rust material
Decal UV
Now I need to place the decal into its proper place
I select the Image Texture of the decal and go into the UV Editing Workspace
Under the Object Data Properties, I open the UV Maps panel
I add a new UV Map and rename it to Decal
I select the faces on the barrel where I want the Decal to appear
I use the U-key to open the UV Mapping menu and choose Unwrap to unwrap the selected faces
I select the UVs and move them
I then use CTRL + I to select the rest of the barrel
I select these faces and move them
I use CTRL + I to reselect the faces where I want the decal
I move the UVs back onto the decal
I then scale the UVs to match the size of the decal
UV Map Node
Back in the Shading Workspace, I add a UV Map Node and open the barrel UV Map
I add a Mix Node between the Mapping Node and the Texture Nodes
I connect the UV Map Node to the Mix Node
I add a second UV Map Node and open the decal UV
I connect the UV Map Node to the Image Texture of the decal and the Image Texture of the decal Normal Map
I change the Extension option of the two Image Textures to Clip