Pantone Formula Guide —> Inaccurate for Letterpress

Hi everyone,

I’ve been having real issues with achieving the right color intensity when I mix inks according to Pantone formula guide.

This usually happens when working with colors that are very light (ie. >80% transparent white, according to pantone formula).

My problem is that my prints are always MUCH lighter than whats indicated on the formula guide. I’ve ruled out the possibility of wrong mixing proportions (tried many many times). I’ve tried on multiple paper types too. Mixing is always thorough.

The final test was a simple 95% transparent white + 5% mixing black. I was getting nowhere near the darkness of what is indicated on the formula guide.

I have also tried replacing transparent white with opaque white. Still the same problem.

I’m thinking that the formula guide doesn’t take into account the fact that
a) inks are a not fully opaque, and
b) letterpress uses a very very thin layer of ink

To reiterate, this seems mostly a problem for color formulas that have large proportion of white in them.

Perhaps I am missing something?

Thanks :)

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I did ANOTHER test and I think I know the problem.

I made the rookie mistake of mixing the white into the color, instead of the other way around!!

Even though I mixed well, I don’t think i was able to get EVERY single bit of the color off the walls of the container, and properly mixed into the white. As such, there was probably a large portion of color still stuck on the walls of the container, even though the rest of the ink was thoroughly mixed.

After thinking about it, I realize how important this is, ESPECIALLY if we are looking at very small percentages of the color.

I guess this is the same not just for white, but for any formula where there is a VERY large proportion of one color.

Hope my mistake helps someone else :)

Letterpress surely lays down a thicker ink-deposit, not a thinner one, than the offset process the Pantone guide is intended for?


my partner told me once:

“With letterpress the ink layer is way thicker than in offset.”

When mixing his inks, according to Pantone guide, he add 50 % of transparent white to correspond!

Don’t hesitate to tell me if it’s true or not, I also need to do some tests!

The Pantone system is based on carefully measured quantities of the inks, usually weighed with a precision scale for small quantities such as would be used for most letterpress printing runs. If you are mixing in a container you risk getting the amounts wrong by percentage as given in the formulas — mixing on a slab makes it easier to be sure all the various colors have been mixed in. You also must use Pantone inks as specified in the formulas.

However, as mentioned, letterpress lays down a much heavier film of ink than does offset, on which the Pantone system is based normally (although there is, or was, a Pantone letterpress swatch book). So using the Pantone system for letterpress, you have to adjust the color formulas for the heavier coverage, always an imprecise process.


Definitely use a slab to mix, not a container. How much ink are you mixing at once?

This might be a silly question, but are you putting enough ink on the press? That could account for the lightness.

Stupid double post. Sorry!

Thanks for the tips everyone!

Summary of things I’ve learnt (hopefully someone else can learn from them):

-Mix on a non porous slab (not a plastic mixing cup)
-Mix THOROUGHLY, smashing and also scraping the slab so you get everything.
-Use larger amounts of ink. Minimum 0.5-1gram per color (if not more).
-Mix smaller proportion inks INTO the larger proportion ink, and not the other way around.
-Ink up the press enough! But not to the extent of over-inking.

Probably the easiest and best “slab” to mix inks on, is a piece of plate glass. Plate glass is thicker than a piece of normal window glass. Get it from a glass supplier who can polish the edges, so they are not sharp. That is a common request for a glass business. Also use two ink knives (or small putty knives, etc.), so that you can scrape the ink off of one knife with the other knife. If you experiment with scraping the ink off the ends and sides of the knives, you can end up with a nice small blob of the mixed color on the glass, which you can then easily move to the press or to a container.

You can also get a pretty good idea of where you are with the color by drawing down a small sample (a speck is enough) of the mixed ink, using a wiped-clean spatula, on the stock you’ll be printing on. It will be a bit darker because of the way it’s applied, but if you scrape firmly and drag it until the ink stops coming off the spatula, the last part will be a pretty accurate example.

To check the color of the ink I’ve mixed, I always roll out some with a small brayer and then roll directly on to paper the paper I’ll be printing on. The finger tapping and draw down method have never been accurate for me.

Awesome advice, thanks!

Previously I was doing a full ink up / clean up to test the ink color!! I will try the new methods suggested.

Right now I am also trying to push the limits on how small a quantity I can accurately mix. I find that 3-5g of total ink will last me well over 200 impressions (for a single color, namecard size)

I’ve invested in a digital weighing scale that goes to 0.01g. However, at such tiny weights, even a slight movement / breeze can mess the readings up, and hence accuracy of the ink proportions.