Vallejo Prussian Blue.

[Harry Faversham]

Very weird stuff, or I've got a dodgy bottle? Black/blue's a very strong and powerful colour. Yet this stuff goes on like a wash, then dries gloss. No amount of mixing makes any difference. Worse bit, even after 24 hours, it lifts when varnished.
One off dodgy bottle, or a crap product?
 

[zemjw]

I have a bottle of that that I've never had problems with it, so it does sound like you got a bad 'un

You could try dropping a stainless steel ball bearing in the bottle, in case the pigment is stuck on the bottom.

I have had mixed success with vortex mixers, eg https://www.amazon.co.uk/Control-Agitator-Shaking-Blender-Laboratory/dp/B092CXYWZW/ref=sr_1_5, but that could be overkill. As much as they're useful, the vibrations really don't settle my hands for the upcoming painting session

[Cubs]

Vallejo is notoriously difficult to mix, even with the most vigorous shaking. The ball bearing is a decent shout, but I'd pull the dropper off and get the end of a paintbrush down there for a really good churn, then put it back on and shake again. This is why I like to buy Vallejo for the price and quality of the paint, but then decant them into paint pots with lids for use.

[Harry Faversham]

Thanks chaps, sounds like I've  got a wrong 'un!
There's two or three stainless steel bbs rattling around in the bottle, doing bugger all!
 

[Dags]

I've had the odd dodgy bottle (assorted colours) over the years - bin it and get a replacement; life's too short to muck around woth something that costs 3 quid.

As an aside, I store Vallejo upside down, allow them to settle, and then just use the pigment. Need to thin more but no need to spend time shaking.

[Dubar]

I hate it when that happens! 

I've been using a fingernail polish shaker I got off Amazon to mix mine up but still have to handshake and sometimes stir with a stick to get some of the Vallejo paints mixed.  Just make sure the top insert and the top are on tight before giving them a spin, I had the screw-on top come off 1 bottle while in the fingernail polish machine but at least the insert stayed put.  I think those inserts with the small hole keep the paint from drying up so fast.

I think I have close to 60 bottles now and so far none have been dried up.  When I first got into this I mistakenly bought a couple of bottles of their paint for use in an airbrush, that stuff is watery thin for brush use.

[Daeothar]

I've found that, especially with the Model Color range, certain Vallejo colours separate quite quickly.  I've got several darker blue and green colours that do exactly the same as you described.

I tend to soldier on and apply a matt varnish after I use one of those colours and that works. But also they're mostly colours I can easily mix up with more compliant paints, so it's rare I use them straight.

As for separation; their oranges in particular are pretty horrible, just like the yellows...

[Elbows]

Either a bad bottle or simply a very old stock bottle.  While I don't have issues with most Vallejo myself, I do add shakers and every year or two I'll add a little medium/water to the bottles to try to keep them hydrated enough, etc.

Occasionally I find myself thinking "Ugh, this beige is too thick..." then realize I've had the bottle for 12 years...

[infelix]

I dug up my old bottle of that color and it seems fine and I haven't really had any problems with them requiring excessive shaking, but then, I'm used to Scale75 paints and they require A LOT of shaking .

[2010sunburst]

Blues drying with a glossy sheen is not unusual in my experience.  I think it’s the nature of the pigment, bit like reds being semi transparent.

[armchairgeneral]

As an aside, I store Vallejo upside down, allow them to settle, and then just use the pigment. Need to thin more but no need to spend time shaking.

Same here