ABOUT AUTO PAINT - SOLVENTS
WHAT ARE REDUCERS OR THINNERS AND WHY DO WE NEED THEM?

Aliphatic hydrocarbons (Mineral Spirits- V M P, Naphtha) Aromatic hydrocarbons (Toluene, Xylene) Esters (Ethyl Acetate, Butyl Acetate) Ketone (Acetone, Methyl Ethyl Ketone (MEK)) Various combinations are used along with other additives such as retarders, accelerators, and levelers to reduce the viscosity of the material to a spray-able consistency and accommodate climatic conditions.
In general, the smaller the molecular size of the resin (high volume solids), the less reducer will be required. Some products require very little or no reduction.
Always follow the manufacturers directions unless you have extensive experience in spray painting automotive finishes. However, in a pinch, the general rule is that reducers are downward compatible. As an example, you may substitute acrylic enamel reducer for enamel reducer, but NEVER vice versa. The solvents are weaker and you could end up with an ugly curdled mess in the bottom of the paint gun.