Car Paint Touch-up

This tutorial is only a way of creating a nice carpaint shader using the mentalray Shader DGS it should be valid for any 3D software that supports Mentalray render ,though im doing it in Maya
I wrote this to share a way of doing a car paint shader with DGS and as a practice for any begginer to play with mray shaders,
its quite basic but gives nice results.

we just need few ingredients for it:
150 gr sugar... ok ignore this....
1- car (yes, seat 600 is accepted
1-Mentalray
2-DGS shaders
1-Francescaluces Mix 8 layer shader
1-sampler info nodes + 1-ramp for faking fresnell effect,you can avoid this by using either a fresnel DGS shader or anyother method for simulating or faking fresnell reflections
1- shiny HDRI image for wowing your neightbours

preparing for cooking:

before dirtiing our hands make sure mix8layers installed properly and working properly

ok, lets take the car model place it over a simple polygon plane floor create a light with shadows (directional is fine)
create one mix8layer shader(in maya: its in multilister---edit--create--mentalray---materials---8mixlayer.
create 2 dgs shaders ((in maya: its in multilister---edit--create--mentalray---materials---DGS_material,
rename one DGS to NACAR and the other to COLOR.
things we should know about DGS,its a realistic material controlled by some 3 main parameters Diffuse GlossySpecular(hence DGS name)+ a shiny value and a transparency,I wont enter in technical details about this shaders, please refer to the many tutorials on the net about them for more info.

the basic idea behind this Car paint tutorial is to mix 2 layers,one will only add strong and quite sharp reflections and speculars+another which will give the color+very spread and dim reflections,now to acomplish this i will avoid the creation of a maya layer shader,it could be done though,but you have to mask transparency values which slow renders quite a lot. im gonna use a different approach,
under the mix8layer options we have tons of cool and nice blending technics to blend diferent shaders, most of them are quite common to photoshop users,
Anyone for a SCREEN blending? the principle is this: Nacar shader will have a BLACK diffuse color and a very sharp reflections in it,this shader will go as a layer on top of the color shader.Color shader will have the color we want to paint the car with applied to the diffuse channel,so if we want green car,just select this color in the diffuse.(Of course, if you want an image as color just put it!!) now,the reflections of this color shader will be very blurry , spread and soft .Color shader will be the base or background layer,by blending the Nacar layer in SCREEN mode on top we will be adding only the reflections,because the diffusion is black.

Now to the practice:
First we need to create the Fresnel fake node,
go to hypershade create a simple ramp and a smaplerinfo node,connect the sampler info FACING ratio to the U and V coord.
now edit the ramp in a way to fake the fresnel reflections properly,bear in mind,ramp values at TOP of the ramp will give the amount of reflection if you where looking perpendicular to the faces of the surface,and values at bottom will give values at faces whose normals are perpendicular to the camera play a bit and get a nice ramp with lower values at top than bottom.