New user. Iwata HP-CS brush. Kroma Kolor food coloring, well watered down for practice. Clarke 'garage' compressor, about 40 psi

Prior use with com-art colours I could get nice fine lines.
Working with food coloring I can 'hear' spluttering from the nozzle. Clean everything. Check with loupe, looks fine.
Needle not bent etc.

When spraying with tip close to the paper, I'm getting a broad line, and ... octopus shaped splashing / spluttering behind the line.

Should food colouring be thinned (water)?
What pressure - 10-50psi mentioned, but nothing definitive, is it the paint thickness that defines the required pressure?

Any help appreciated.

paint thickness does have bearing on the pressure used, to thick and not enough pressure and it wont flow, to thin and too much pressure results in the octopus shaped "spidering" that you talked about, food colouring is a hell of a lot thinner than even com art, its basically coloured water so firstly try reducing your pressure, you could probably get away with between 5-15 psi (but dont quote me on that).... does the pe2 in your name refer to your post code??
ps i wouldnt imagine that food colouring needs to be thinned, your brush doesnt have the smallest nozzle available so it should flow through with very littlle trouble
Thanks for that. Makes sense, high pressure, low viscosity = 'spidering' (if that's the right term).
I guess I was just being mean watering down the food colouring and made it too thin.

Yes, PB, bit W but still Cambs!
Fezzles, I'm almost disappointed, a thread titled splatter, and no rudery Lol. I was expecting a comparison to a plasterers overall at least. LOL!
No the food coloring is VERY thin as it is in the bottle. Don't thin it anymore! Also, beings theres no chance of tip dry you can take your pressure down and I mean WAY down, 5-10 psi. I would also thin out the food coloring with vodka, everclear or gin, if I had to, not water. But then again, I wouldn't even bother reducing anymore than it is.
Another thing I've found, is if you're using an airbrush with a larger nozzle/needle you're not going to get the atomization necessary for a nice clean line. Especially at the low, low pressure.
A .2 or finer is definitely better for the Airbrush Food Colors.

(cake decorator for 8 years roundabout).
I agree it sounds like the food color is way too thin for that pressure. The CS has a .35 needle which is much more suited to textile and automotive type paints. For food color that you would use for cake decorating I would be more apt to use a Iwata B or A with about 5 psi. The CS shoots a lot more CFMs than a fine art brush so even with lower air pressure you may still have trouble. Its like taking an air gun like an HVLP with a large needle at 10 psi. Loaded with Wicked color sprayed at a hard surface. You can't get too close or you will have runs and spiders even though you are using 10 psi. Now put the same paint into you CS with a .35 needle and it consumes a lot less CFMs at 10 psi. You will notice a total different reaction from that paint with no spidering or runs.

Keep On Painting

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