Tamiya XF-23 gumming up airbrush

It's strange that it's gumming up, given that you're using Iso as a thinner.

I still use some Tamiya acrylics from about 1982-85, so it's (possible, but) unlikely to be an age issue. especially if the paints have not been subjected to extremes of temperature (ie. stored indoors at average room temp).

Having said that, I have, on occasion, had one or two bottles which have "gone off" in the jar and though still liquid (or semi-liquid), when stirred throroughly and reconstituted to a usable consistency, looked like a suspension of grains of cured paint rather than a usable paint. 

2:1 thinner to paint is an acceptable mix. I have seen it suggested that when using a retarder, mix it with the thinner first before adding to the paint, rather than mixing the  paint/thinner and adding the retarder afterwards.

Your thinning process show a well formulated step from experience. Could that be possible that it is not the paint itself, but it may interact with what was left in the airbrush after the previous painting?

What brush is that and how you cleaned it? I have seen MM acrylic turned into a glob of glue when touched with Polly S airbrush thinner. Just a wide guess.

Now, I use Tamiya X-20A thinner with Tamiya acrylic only and clean the airbrush more thoroughly when change brand of paint.

I use a Badger 105. After use, I flush out the airbrush with windex, followed by some distilled water to get the windex out, and then usually rub the bottom of the cup with a cotton swab with some windex on it, and then wipe the needle down, and then spray some distilled water out of it again..I might try some of my other Tamiya paints tonight, and if the problem continues, I'll completely strip down the brush and give it a good clean.

spitting is usually caused by not thinning enough or brush needs to be cleaned. when using acrylics i clean my brush right after use because once it drys its a pain to clean. 

My Tamyia white does this every time. I have no probles with any other color, I think I may have a bad jar.

I use regular old laquer thinner with Tamiya paints and they spray beautiful. Try tis put some iso on a flat surface and blow air at it with your airbrush what happens it drys very quickly. Thats why your tip drys up with paint. I went to enamels for everything until I found out I could thin Tamiya with Laquer thinner and clean the brush with it. I use Tamiya more and more now.

Bill

 I think the issue is due to your choice of thinner. I know many people use Iso Alcohol and I to have used this in the past. IT IS NOT THE BEST WAY. What you are experiencing is that you paint is drying in the brush. You may also notice a "dusty" appearance on the models surface, this is because the paint is drying in the air before it hits the models surface. These issues can both be corrected by using a laquer thinner instead of ISO Alcohol.

 What you need to use as a thinner is a laquer thinner. You can by these from Mr Hobby, Gianotes, & Tamiya makes one as well. Be sure to use the Tamiya thinner with the Yellow cap. Tamiya paint is not a true acrylic. It is in fact a synthetic laquer.

 If you would like to use an acrylic paint. Take a look at Vallejo Acrylics. These paints can be thinned and cleaned with tap water. Vallejo also produces a line of paints named "Model Air", these paints can be used WITH OUT thinning at all. They go straight into the AB the way they are.

I hope this is helpfull and answered more questions than it produced! Please let me know if I can help at all in any other way.