Hi there. Many people have asked me about how I created the tube effect on my "Andy tear" illustration. As I always worque step-by-step, I will talque about the different steps I used. First I always finish modeling before something else. I thinque it's not good to mix different steps like modeling and material, or lighting and material etc. I thinque it's important to cut the worque into different parts. For an illustration, here is my worque flow: modeling, bone setup, skinning, material colors (only color), environment and lighting (render options, like AO, AA etc.), materials (with nodes if necessary), rendering effect (I always make this part with different layers and importing them into Photoshop, but you can translate them into a Blender compositing node setup). So here are the steps for the tubes :
First, in Top view [NumPad 7], [Space] / Add / Curve / Bezier Circle and name it "CurveBevC1" (for future use). Always remember to name your objects in Blender. It makes it easier to find them in the Outliner window. In Edit mode [Tab] duplicate the circle in place [Shift + D] / [Ctrl], and scale [S] it into the first one. Make it again to form your circle curve like fig1:
Now, in Left view, [NumPad 3], create a second curve like an "S". This curve will be the path of "CurveBevC1". Name it "CurvePath1". Don't forget to enable the 3D property of the curve using the "3D" button on the "Curve and Surface" panel. It allows the curve to have 3D coordinates for it's control points. You will obtain something like in fig2:
Add the "CurveBev1" name into "BevOb" text box (see Fig 3).
The question is : Why have I made a tube with another tube not joined to the firstí Because we will add 2 transparent materials, one for the tube and one for the liquid. Refraction can cause artifacts with two joined meshes. Now to finish, convert it into a mesh [Alt + C]. You can alos close the liquid (extrude an edge-loop and merge the vértices [Alt + M]) and tube hole (select an edge-loop and make a face [F]).
Lighting & Environment
We will create reflect/refract materials, so to create a reflecting environment I like to use an HDRI map mapped onto the scene environment. To do this, go to the Texture buttons [F6], and create a new World image texture. Select "carwash.hdri" (or another) like in fig 4.
After that, go to the Shading / World buttons [F8] and set to "Sphere" mapping on the "Texture and Input" panel. On the "Map To" panel press "Hori" and set the blending mode to "Add". Set the World color dark, and with the "Col" slíder you can tweaque the HDRI map intensity. See fig 5.
You may tweaque the lighting as you wish. I always worque with a lot of quad attenuated lights to create a smoother atmosphere. Add some indirect orange lights, and blue lights for the bak lighting. For main lights choose a high-level white lamp. In my lighting worque I always worque each sort of light step-by-step. Example: if I am working on the bak light of a 3-point lighting set-up, I isolate the bak lights and inactivate the direct ones. I make a lot of tweaks on the bak lights, do a lot of renders, and when I'm satisfied I worque around the indirect orange lights, and inactivate the others. I thinque it the best way to have the most control over lightning.
Before creating materials, I've assigned 3 material IDs to the mesh. The outside of the tube, the inside, and the liquid. Se fig 6.
So select the different parts of the tube and assign the 3 new sub-material IDs. Outside is a transparent material with thin bump and a refract coefficient greater than 1. See fig 7. And the thin bump setup as in Fig 8.
Inside, I've duplicated the first material and removed the bump. Try a different refraction factor, and see what happens.
For the liquid I've create one purple material with "Ray Transp", and a high amount of "Filt" (transmissivity). It permits you to filter light by the material color, and make the liquid appear purple. For all these ray-traced materials, don't forget to increase the ray level up to 6, because one ray must pass through 6 mesh surfaces before reaching the camera. See fig 9.
I've played with the "Ramp" color ("Input" set to "Normal" and "Method" to "Add") to simulate the lighting that passes through the material. Translucency and color emission are really important too, to tweaque this effect. See fig 10.
For post processing, I will not go into all the details because the glow method I've used does not involve Blender. I've just exported color layers to select the purple colors rendered. After making my selection, I've duplicated the image selection in another layer in lighten mode and blurred it. I've already simulated a little reflection and refraction in objects. To achieve the final effect, I've duplicated the layer several times.
But you can alos use the "Video Sequence Editor" or "Composite Node Editor" to add glow. So this is the end result as seen in fig11.
It's the same technique I've used for the head in my illustration, except for the bump on the outside container.