Printed Uncoated PMS on Coated Stock
I did my artwork on the uncoated PMS colours as I originally planned to print it on uncoated stock. We ended up changing the stock and there was the forgetfulness of one person to not change the PMS colours.
The colours (well mostly the gray) are very light. So my question is, if I change to the coated colours, will the colours be even lighter or will they be darker?
The reason I ask is because it's packaging, and I am using two different companies and the other uncoated stock needs a big adjustment as it's printed on quite dark white paper and since I am using gray it makes a lot of difference.
I also didn't want the gray to be so light as it should be closer to the Pantone book.
A Pantone specification is a Pantone Specification. Pantone ink formulas do not change based upon coated (C) or uncoated (U) stock.
The Pantone specification books all print the same ink colors. The difference is how that ink looks on different stock -- C or U -- not the actual color of the ink. Uncoated stock absorbs more ink. So there is a natural pigment change when printing on uncoated stock. Coated stocks absorb less ink so colors tend to stay more opaque (or solid).
The digital color books appear as different colors for the same reason -- they are different so that on screen there's a better visual representation of how that ink appears when printed, but it is still the same ink formula. And that same formula is used on press. To the pressman, there's no difference in the ink he/she grabs between Pantone C and a Pantone U -- it's just Pantone Warm Grey 5.
So, in short, there's no reason to switch from something like Pantone Warm Grey 5 U to a Pantone Warm Grey 5 C. It's the same ink. The only possible caveat is to switch to a C color so that your digital file better visually represents the final printed piece, but there's no technical reason you need to switch from a U color to a C color.
Look at a Pantone color guide and check your colors to see how they will look on coated stock.
If then, you are unhappy about how the color appears you may need to change the actual Pantone value to a different color entirely. I.E. if you are unhappy with how dark Pantone Warm Grey 5 appears on coated stock, you may want to change to Pantone Warm Grey 4.
Ultimately, for color critical work, you should get (or ask for) a color proof or Chromakey for the job so you can verify colors before anything is actually run. Note: Not a PDF proof.. an actual hard copy color proof. Most decent press houses can FedEx overnight a proof to you and you can FedEx it back.