Model Master Question.

Some of the MM colors are thinner than others, I have noticed some are thin enough to spray on their own and others not... I think with the yellows and whites especially they are thin by nature.. (sand being in the realm of those somewhere) ... when I used them I could spray some straight from the bottle, others needed various amounts of thinning... it was pretty much trial and error for which needed what...

I have noticed that with the Acryl line but not the enamel ones.
Is it that thin even after thorough mixing?
I was thinking maybe the pigments had settled to the bottom when you mentioned it being thin.

I have noticed that with Testors enamels also. Some are so thin I need to brush a second coat, while others are so thick I almost lose the detail in the plastic.

I haven't gotten around to airbrushing yet. But when I painted cars, we wouldn't count on just a standard mix ratio, even within the same paint line. We would always do a drip test with the paint stirring stick, cheaper than a viscosity gauge.  

They usually are not that thin, typically being pretty decent from the bottle for brush painting, but there will be sample to sample varaiation.  Ironically, I too had a bottle of sand that airbrushed perfectly straight from the bottle, but I also another that was normal and needed thinning before airbrushing.  I've had other paints that were so thick, I needed to thin prior to brush painting.  It's because of this variation that I consider the concept of an airbrush thinning ratio to be worthless.

Well I bought some forest green to spray on the Abrams instead, and it sprayed perfectly from the bottle with no thinning at all, just some warming up with hot water and stirring, I bought another bottle and the exact same consistency as the Sand and previous bottle of forest green, made things alot easier for me lol

I thought their Enamel II line (all numbered 2000+) come pre-thinned and ready for airbrush.  Shouldn't happen to Sand though.  I just sprayed their Zinc Green Chromate two days ago and it needed 3:2 paint to thinner for it to be laid down right.  It was giving me spiders when I did it 1:1 in ratio.

I havent sprayed the Sand, but its consistency is very thin already, and the forest green layed on absolutely perfect, no thinning at all. maybe I just got lucky? lol

This is true with the Model Master II colors.  These colors are or (were)  mixed in batches outside of the US, and when Testors discovered that a higher solvent content was added, they liked it, thus MM II colors are thinner in viscosity and most of the new FS colors are airbrush ready.  The MM II figure colors were manufacured a bit thicker for superior brush painting characteristics.  *Source: Testors Technical Manual.