GRACol and uncoated

[longlimb]

So would it be safe to say I would want to shoot for the same dot gains for uncoated as I did for coated? I arrived at a very decent gray for coated, so would I want the same dot gain for uncoated but with the lower SID's?

[gordo]

So would it be safe to say I would want to shoot for the same dot gains for uncoated as I did for coated? I arrived at a very decent gray for coated, so would I want the same dot gain for uncoated but with the lower SID's?

You want the same final tones in your presswork, it will take different dot gains to get there.


best, gordon p

[longlimb]

Would you say an uncoated TVI is typically lower or higher than coated ones? I'm getting ready to do an uncoated press calibration in the morning and I have the GRACoL target dot gains for coated "in a perfect world" but I don't see anything for uncoated.

Basically, if I use the same target curve that I used for coated to do my uncoated plate curve, will the uncoated sheet be close granted some adjusting might need to be made?

[roger]

uncoated vs. coated sheets:
thicker ink film on the rollers,
lower solid ink density on the sheet,
higher dot gains (TVI) on the sheet

you will be targeting higher dot gains with uncoated. If you target the same dot gains as you got for coated, the imagery and spot color builds will be too light/thin.

Roger

[longlimb]

So with my coated plate curve I have, I am getting around an 18% dot gain at the 50%. I wouldn't want that same amount with uncoated?

My uncalibrated press run will obviously have way higher gains. But wouldn't I still want to shoot for that 18% gain at the 50% like I did on the coated?

Example:

Uncal Coated 50% screen reads 72 - so I cut back the 50% area on my curve by 4 so I would hit my 68 (18% gain)
Uncal Uncoated 50% screen reads 77 - so I would cut back the 50% area on my curve by 9 so I would hit 68 (18% gain)

Is this what I would do, right? Roughly of course...

[meddington]

So with my coated plate curve I have, I am getting around an 18% dot gain at the 50%. I wouldn't want that same amount with uncoated?

Keep in mind that TVI is a a value calculated from the solid density and the density of the particular percentage your measuring. Since with uncoated, your solid densities will be lower, your TVI will have to be higher in order to have the same tone at 50% as a coated print. One of the reasons that targeting TVI is a bit ambiguous.

Uncal Coated 50% screen reads 72 - so I cut back the 50% area on my curve by 4 so I would hit my 68 (18% gain)
Uncal Uncoated 50% screen reads 77 - so I would cut back the 50% area on my curve by 9 so I would hit 68 (18% gain)

Again, because the solids density is lower, doing the above would give you a lighter tone. A better method would have you matching tone response based on density rather than TVI, and determining which input dot value yeilds the density tone and adjusting from there. The G7 method is an option, or visit Gordo's blog.

You could also aim for ISO 12647-2 TVI curves for your particular paper type.

[longlimb]

Ahh. I think I understand. Thanks meddington. So how do I know what is a good dot gain to shoot for with uncoated and GRACoL? Is there not one for uncoated? Is the ISO 12647-2 curve a better way to go when talking about uncoated?

[gordo]

Ahh. I think I understand. Thanks meddington. So how do I know what is a good dot gain to shoot for with uncoated and GRACoL? Is there not one for uncoated? Is the ISO 12647-2 curve a better way to go when talking about uncoated?

Dot gain is NOT the issue. For the purposes of your question, there is no "good" or "bad" dot gain to shoot for.
You are shooting to align the final presswork tone values. I.e. for a 50% tone request in the original file you should achieve the same 72% on both coated and uncoated sheets. It basically does not matter what the dot gains are - as long as you achieve the desired tone on press.
These two blog entries explain the process - in the context of printing at higher SIDs - the principle is the same though.
http://qualityinprint.blogspot.com/2...xx-part-3.html
http://qualityinprint.blogspot.com/2...xx-part-4.html

best, gordon p

[longlimb]

You just answered my question. Sorry I don't think I asked it very well. I know my curve will be different. But if 72% at the 50% screen is what I ended up with on coated, then 72% is what I would want on uncoated as well... even with lower SID's.

Thanks guys!

[gordo]

You just answered my question. Sorry I don't think I asked it very well. I know my curve will be different. But if 72% at the 50% screen is what I ended up with on coated, then 72% is what I would want on uncoated as well... even with lower SID's.

Right, and don't forget - you can always raise your SIDs on uncoated to determine the optimum SIDs you can run with (along with good plate curves) to get the best result possible from your process.

best, gordon p