Since I last posted, I have also tried thinning Tamiya acrylics with lacquer thinner. I've read that some have used it to thin Tamiya acrylics for airbrushing, with good results. I used the same processes as I do with Tamiya's own thinner. I put a couple of drops of lacquer thinner in a well in my palette, and then dipped my brush in the paint, then into the thinner, and applied the paint; I mixed a couple of drops of lacquer thinner in a well, and then added a couple drops of paint, stirring with a toothpick till it was consistent, and then applied it to the piece; and I've also dipped the brush in the thinner, and then into the paint, and then applied it. In each case, I got a nice, flat coat, no clumps, pretty much as I do with Tamiya's own thinner. So, if you don't have Tamiya's thinner but you have lacquer thinner, you could try that, too.