Opaque white ink going yellow

Dear All, any ideas why my white ink is going yellow? It’s a 1kg tin of Van Son litho ink. About two years old. I am (fairly) certain I haven’t polluted the ink with a dirty palette knife. But the studio was uninsulated for the first year so it would have experienced hi and low temperatures.

Does this just happen over time? Or is there a likely cause for this?

Thank you

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You do not state whether this is rubber-base or something that makes a skin. A skin on an oil- or pyroxylin- or other base is the result of the varnish in the surface of the ink oxidizing. If a skin is present, drawing it back will reveal if the ink itself has changed color (I cannot imagine it doing so, unless it is livering). Part of the composition of non-rubber-based inks is a varnish, which polymerizes in the presence of air or on a surface for which it has an affinity. If the ink below the surface film has not changed color, then there would be no problem with the balance of the can.

Hi Frank sorry for the slow response. I believe the ink is oil based that is what I usually buy, but strangely this one has no skin on it despite being two years old. Deeper down in the ink it is less discoloured (but still yellowing) so this would suggest oxidation of the varnish like you say. I’ll attach a couple of shots of the ink.

Do you think this is just an odd imbalance of ingredients? Just wondering if I buy another tin will it do the same?

Anyone got a recommendation for a white I can use to go over other layers of ink that doesn’t yellow?

Thank you

Shots of the ink

Thank you

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It looks to me like it might be separating (insufficiently milled). One solution would be to turn it all out onto a CLEAN slab, and, with a couple of eight- or ten-inch ink knives, mix it all thoroughly. The best treatment would be to turn it all out into an ink makers’ roller mill (dang, now I wish that I’d bought one, while I had that opportunity!), and thoroughly whip it back into shape. See if twirling it around some in the can has any result; let that be your guide.

Thanks Frank, I gave it a swirl the other day it certainly made it whiter (also made bubbles rise like mixing pancake batter). And thinking about it when it was left running on press rollers for a while it did get brighter then - so maybe that’s the way to go - leave on press for a bit first rather than hand inking

You reckon it’s just a duff batch or are there other brands/types of ink to try?

Thanks for the help

I’d try another brand of opaque white. And if this is oil-base, but didn’t skin, I’d be awfully careful about putting it on anything that might give any kind of problem; i.e: multiple trims, folding, overprint, etc., etc. It should not have separated like that; it looks like the way some metallic inks separate, and the treatment for them is the same as I suggested for this white. Work this one off as a ground for colors where the white is a minority item in the mix.

I agree with everything Frank said.

1. Make a little test print and check for the problems Frank mentioned above.
2. If the test goes ok, work off the white in other formulas.
3. If you really need to use that white, you might try adding a very small amount of a red shade blue like PMS 072 (or reflex, or maybe even violet). That should kill the yellowness in the white. (Try a very small batch first).