Chrisk-k
Tamiya paint does not contain a retarder or a flow aid. Tamiya thinner does contain a retarder.
Which products contain what additives wass not my point. My point was that even if they do contain retarder, it may not be enough and it's OK to add more if you'd like. I was disagreeing with a message that said there was "no need" to add retarder or flow enhancer. But if you are technically curious like me, read on for proof that most Tamiya paints contain a retarder.
Have a look at MSDS sheets for Tamiya acrylic paints. Then have a look at the MSDS sheet for Tamiya's acrylic retarder. The retarder's only ingredient is something called "3-methyl3-methoxyl butanol." Look at the MSDS sheet for any of Tamiya's acrylic paints, such as deck tan or flat black. You will see that all of these paints (except one or two metallic paints) also contain the same ingredient in Tamiya's retarder. (Some colors have more than others.) Proof that Tamiya's paints do, in fact, contain a retarder.
I don't know if Tamiya's acrylic thinner has a retarder because I don't have an MSDS sheet for that product.
I'll plead ignorant on the flow enhancer because I don't know what substances serve that purpose. For all I know, the retarder also acts as a flow enhancer.
Chrisk-k
A WN retarder is for water based acrylics and Tamiya paints are alcohol based. So I am not sure about mixing them.
I wasn't sure either until I tried it (I am a big advocate of testing before actual painting). It turns out that Tamiya acrylic paints contain both water and alcohols. Again, see the MSDS sheets. Most of the alcohols found in hobby paints/solvents (4 carbons and less) are water soluble if not fully miscible. So there isn't a problem mixing the two.
Many modelers thin Tamiya with 70% or 90% isopropyl alcohol and it works fine. IPA comes in mixtures with water, that's what the percentage means. So these modelers are actually thinning with both alcohol and water.
Chris