SM52 extreame dot gain on black unit

[RGPW17100]

I am running a SM52 5 color with coater. Regular conventional screening at 175 I have minimal dot gain mainly in the black unit. I am running KCMY units 2 thru 5. We use a hybrid screening called Specta and this is run at 300 dpi. I gain heavily on the Black Specta unit (unit 2) where a 75 percent screen is gaining to 95 percent. If I switch out the Specta plate for a conventional 175 line screen my gain is minimal and can get pretty close to the proof. I have checked roller stripes and rollers are about 6 months old. I run alcohol at 7 percent and we are using Fuji thermal plates. Can I expect to hold a 300 line screen on coated and uncoated stock? I am trying to make a switch on press to run YCMK to see if repeated hits on blankets 3 through 5 may be causing some of this gain however I keep getting reprints of jobs and fear the sequence change will make the final print different.

 

[gordo]

I am running a SM52 5 color with coater. Regular conventional screening at 175 I have minimal dot gain mainly in the black unit. I am running KCMY units 2 thru 5. We use a hybrid screening called Specta and this is run at 300 dpi. I gain heavily on the Black Specta unit (unit 2) where a 75 percent screen is gaining to 95 percent. If I switch out the Specta plate for a conventional 175 line screen my gain is minimal and can get pretty close to the proof. I have checked roller stripes and rollers are about 6 months old. I run alcohol at 7 percent and we are using Fuji thermal plates. Can I expect to hold a 300 line screen on coated and uncoated stock? I am trying to make a switch on press to run YCMK to see if repeated hits on blankets 3 through 5 may be causing some of this gain however I keep getting reprints of jobs and fear the sequence change will make the final print different.

Lots of things to consider - assuming you're using Spekta 2 screening.
First, yes you can expect to hold a 300 line screen on coated and uncoated stock.
Are you using a dot gain compensation curve in plate imaging to normalize your tone reproduction?
Do you have a USB microscope so you can take snaps of your printed dots? The scope is cheap and will tell you a great deal about your ink laydown as well as whether you have an issue with slur, doubling or ink transfer.
Were you printing successfully with Spekta and now you cannot?
Switching to a YCMK sequence is a severe move and not standard for sheetfed - I would suggest that you figure out what's going on first.

best, gordo

 

[RGPW17100]

Are you using a dot gain compensation curve in plate imaging to normalize your tone reproduction?

We are using a G7 P2P target to establish our plate curves. Not sure if this is what you are asking. When I print the P2P target I am able to match the color proof however there is not much Black screening over 70 percent in any of the photos.

Do you have a USB microscope so you can take snaps of your printed dots? The scope is cheap and will tell you a great deal about your ink laydown as well as whether you have an issue with slur, doubling or ink transfer.

No to this. We only have loops that are 20/1 resolution.

Were you printing successfully with Spekta and now you cannot?

Our main operator left about 6 months ago but we have always had issues with Specta. Lots of jobs have required going to a conventional black plate to reduce the gain. We have an older 40 inch Speedmaster from the 1980s that is able to print specta with little effort however he has trouble doing some of the matches from our proofer.

Switching to a YCMK sequence is a severe move and not standard for sheetfed - I would suggest that you figure out what's going on first.

This is an attempt to see if one unit prints better then the other. Not a permanent fix just to see if we can find it this is a press issue or a plate issue

 

[gordo]

Are you using a dot gain compensation curve in plate imaging to normalize your tone reproduction?

We are using a G7 P2P target to establish our plate curves. Not sure if this is what you are asking. When I print the P2P target I am able to match the color proof however there is not much Black screening over 70 percent in any of the photos.

I don't know. For me tone reproduction is separate from color.

Do you have a USB microscope so you can take snaps of your printed dots? The scope is cheap and will tell you a great deal about your ink laydown as well as whether you have an issue with slur, doubling or ink transfer.

No to this. We only have loops that are 20/1 resolution.

Loupes are great, but being able to share what they see is priceless for analyzing problems. Buy one. They're cheap enough.

Were you printing successfully with Spekta and now you cannot?

Our main operator left about 6 months ago but we have always had issues with Specta. Lots of jobs have required going to a conventional black plate to reduce the gain. We have an older 40 inch Speedmaster from the 1980s that is able to print specta with little effort however he has trouble doing some of the matches from our proofer.

OK, Spekta has a different gamut than 175-200 lpi AM. So, if your proofer was set up to the gamut of a conventional screen then you'll have problems matching the proof with Spekta. TVI/dot gain is a simple issue of creating a dot gain compensation curve applied to the plate.

Switching to a YCMK sequence is a severe move and not standard for sheetfed - I would suggest that you figure out what's going on first.

This is an attempt to see if one unit prints better then the other. Not a permanent fix just to see if we can find it this is a press issue or a plate issue

No need to change ink sequence. Just look at your dots under magnification and you should see if there's any unit to unit distortion.

best, gordo

 

[RGPW17100]

Moved Black to unit 4 as a test and this unit is printing a bit cleaner then unit 2 however the print still looks nothing like the proof. I forwarded this thread to our prepress supervisor about the color gamut using specta versus conventional. We are going to have a struggle with this cause I guess our plate reader will not accurately measure specta but does measure conventional. Another issue I don't understand is Prepress is telling me the same G7 curve is used for both uncoated and coated. I cant believe that I can match a G7 proof using the same set of plates on a coated and uncoated sheet.

Gordos can you give me a link to a USB microscope or give me a make and model so I can google it?

 

[gordo]

Moved Black to unit 4 as a test and this unit is printing a bit cleaner then unit 2 however the print still looks nothing like the proof. I forwarded this thread to our prepress supervisor about the color gamut using specta versus conventional. We are going to have a struggle with this cause I guess our plate reader will not accurately measure specta but does measure conventional. Another issue I don't understand is Prepress is telling me the same G7 curve is used for both uncoated and coated. I cant believe that I can match a G7 proof using the same set of plates on a coated and uncoated sheet.

Gordos can you give me a link to a USB microscope or give me a make and model so I can google it?

Here's the one that I use: 2 0MP USB Digital Microscope 25x 200x Magnifier Video Camera w Measure Software | eBay

There are many similar. I paid $75 at our local drug store (London Drugs) so that I could easily return it if it didn't meet my needs.

20x-200x is more than adequate for print application. Here, for example, is what dot doubling looks like under the scope:

There are several variables you might be dealing with as far as aligning your presswork to the proof beside ink transfer issues. Assuming that the base hues of your process colors are correct...
• Spekta may have a different on-press dot gain response than your regular AM screening and a proper dot gain compensation curve may not have been created/applied.

• You may have an OBA (Optical Brightener Agent) mismatch issue. Proofing papers tend not to have OBAs. Press papers tend to include high levels of OBAs. Press ink is somewhat of an OBA blocker so, depending on the amount of UV light under which you are comparing proof and presswork (the light in the light booth as well as ambient light spilling into the light booth) the color in the presswork can shift - sometimes dramatically - compared with the proof. This disconnect tends to primarily manifest in the pastels - whites to approximately the 70% tone.
( The Print Guide: The issues of Optical Brightening Agents in paper and ink )

• This is what the Spekta 2 (which I assume is what you're using) screen patterns look like:

The Black reacts on press somewhat like a conventional AM screen. The C, M, and Y patterns are more like other 2nd generation FM screens (Staccato, Taffeta, Segundo, HDS, et. al.) The result is a difference in hue whenever screen tint builds contain one or two colors (C, M, Y, CM, MY, CY). If the profile for your proofer is based on an AM screen then there will be an automatic color disconnect with Spekta.
( The Print Guide: AM and FM gamuts compared )

• Reading the plates is a separate issue. You measure plates to ensure that the platesetter is delivering consistent dots on the plate. You can use a conventional screen to determine if this is happening. The other reason to measure plates is to ensure that the correct dot gain compensation curve has been applied. You can check that with a densitometer. You need to create a bitmap of an 11 step step wedge that has the compensation curve applied. Then image that bitmap above a greyscale stepwedge. The bitmap wedge is unaffected by the RIP. The greyscale wedge will have the curve applied. If you can see a difference between what should now be matching patches on the plate then you know that the curve has not been applied. You can also measure the plate with a densitometer.
( The Print Guide: Using a densitometer to measure plates )

What you've got to do is isolate each potential point of failure and determine which one is the cause.
Try to avoid making statements like "this unit is printing a bit cleaner". "Cleaner" is a meaningless term. Print production is a deterministic by the numbers manufacturing process. Try to translate qualitative terms ('cleaner') into quantitative terms (e.g. our dot gain on the magenta unit is 10% lower than our shop standard).

RE:

I cant believe that I can match a G7 proof using the same set of plates on a coated and uncoated sheet.

I agree.

Hope this helps. Best, gordo

 

[JenC]

Lots of things to consider - assuming you're using Spekta 2 screening.

Sorry to jump into this conversation so late - I work in the prepress department here. We're not using Spekta 2, just regular Spekta. Would that change anything in your response?

RE:

I cant believe that I can match a G7 proof using the same set of plates on a coated and uncoated sheet.


I agree.

Our G7 people said it was common to have a set of lower print densities for press to match the uncoated proofs instead of making a separate plate curve for them. Is this unusual?

(Thanks for the great info, gordo - very helpful.)

 

[RGPW17100]

So we ordered a usb Microscope. JenC is our prepress supervisor. With the loop we are using it appears some kind of slur or noise is in the dot area. We will know more when we get the microscope. We are burning a plate for our GTO to see if the same effect is happening then I will hang the the SM52 plate on the gto and do a comparison. Our old 40 inch Speedmaster is not having the same problem that I am having on my press. I run a 5 mil plate and he runs a 12 mill plate and I am wondering if there might be something there. The GTO plates are 12 mil as well. We are not using Specta 2 because our sales and press team did not like the results of it so they stayed with just Specta

 

[gordo]

Sorry to jump into this conversation so late - I work in the prepress department here. We're not using Spekta 2, just regular Spekta. Would that change anything in your response?

Our G7 people said it was common to have a set of lower print densities for press to match the uncoated proofs instead of making a separate plate curve for them. Is this unusual?

(Thanks for the great info, gordo - very helpful.)

AFAIK Screen has only published images of the black printer pattern for Spekta 1. If you can capture the screen patterns of the other channels and post them here I can give you more info.

G7 is a methodology (to grey balance a process) not a print specification. Most "quality" sheetfed printers will have different SID targets (usually higher) for printing on uncoated sheets vs coated sheets. They may or may not profile that print condition so that their proofs better reflect the final presswork. Basically, "quality" printers optimize their presswork to get the best possible results given the limitations of the process. So, at the very least they'll have press curves for gloss coated, matte coated, and uncoated substrates.

best, gordo

 

[gordo]

@RGPW17100
The presswork dots need to mimic the plate dots. (seems pretty obvious but most printers miss this connection)
When you get your microscope take a snap of the dots of a specific tone on your 5 mil plate and your 12 mill plate. Say a 40% tone. Then take a snap of the dots in the presswork that result from those plate dots.
If everything is working properly they should be very similar.
Post the images so we can have a look at what you're getting.

best, gordo

 

[RGPW17100]

We printed a job that we did in January that has a black specta gradient. Back in January when I printed it the specta screen printed almost solid black. Looking at the plate I can see that the Kodak proof does not represent the plate. Just looking at the plate and the proof we can see that the plate curve or the Kodak proof is wrong. We just received the USB microscope today. Will take a few days to figure out how to use it and get some pictures posted. I am not going to waste time doing print tests on the GTO versus the SM52. We should be able to evaluate the difference if there is any from the GTO to the SM52 with the microscope and our loops. My dot gain on press does not seem to be our problem. Our plate curve for the SM52 seems to be the problem and does not match the G7 Kodak proof. We will hopefully compile better information within the week.

 

[gordo]

Looking at the plate I can see that the Kodak proof does not represent the plate. Just looking at the plate and the proof we can see that the plate curve or the Kodak proof is wrong.

What kind of Kodak proof are you using? Is it a dot proof like the Approval or Spectrum?

gordo

 

[RGPW17100]

I spoke with Jen in Prepress and she says our proofer is not Kodak. I was sure it was awhile back when we were using CGS and Oris.

We received the USB Microscope and I have been measuring dots on different test plates. I uploaded this file to my Comcast online storage. The left picture is our current G7 curve. The middle one is the G7 curve obtained with a G7 master almost 2 years ago. The picture on the right is our old 40 inch press that has the original G7 curve from 2 years ago. Our main press operator quit and had a problem with the original curve printing too red. He had prepress output P2P targets and at that time from what he printed became the new G7 curve which is on the left of my upload. This was two days after he left. I noticed I was printing dirty and having all kinds of problems with dark black screens. When we changed our curves 4 months ago something went wrong with the black curve. My guess is G7 mainly focuses on the CMY and has very little to do with the Black. From the use of the microscope I can see my black is really jacked on screens above 50 percent. For the time being we have gone back to the original plate curve that was established for the press when the G7 Master ( I believe this is the correct term for the G7 guru). We are going to try the P2P target again and see where that leads us. http://home.comcast.net/~printergod2000/microscope%20test%20jpeg.jpg

 

[gordo]

Could you post some micropics of the same tone, say 40%, of your press sheet of the k, c, m and y for comparison?

Thx, gordo

 

[RGPW17100]

I will see what prepress can do. Do you want the plate pics or do you want the printed sheet pictures?

 

[gordo]

I will see what prepress can do. Do you want the plate pics or do you want the printed sheet pictures?

Let's rewind the tape.

You need to confirm that the tones you require are imaged on the plate as requested. I.e. if you ask for 50% on the plate then you should get 50% (+/- ~ 2%) on the plate for each color. If there is a tone reproduction curve being applied to the plate then you should get the expected tones on the plate. Those tones may be different for each plate - but they should still be the ones that are expected. A plate reader or densitometer will tell you if the tones on the plate is as expected (or not).

Once you know the plates are correct then you look at the resulting presswork.
The dots in the presswork should mimic the dots on the plates. Here's an example of what that looks like. Plate on the left presswork on the right:

Not too bad. But if this is what you see:

Well the dots in the presswork don't look like the dots on the plate. That tells you there is a press problem. In this example, note the drops of water in the solid black ink, the fuzzy edge of the dot as well as the spread of the dots. This may indicate, over-emulsification, over aggressive fount solution, etc.

Examining the image of the press dot (as well as solids and overprints) can suggest what the press problem is.

So, what you need to post is a photo of the plate dots for CMY and K as well as the press dots for CMY and K. Comparing the dots of the K vs the other colors helps to confirm that the problem is press rather than plate related.

best, gordo

 

[RGPW17100]

Our plate reader has problems reading specta dots. To do this test we will have to use conventional 175 line screen in order to read the plate with the plate reader. I will try and get plates today. Both specta and conventional.

 

[gordo]

Our plate reader has problems reading specta dots.

You could try using a densitometer to read the plates since it does not look at the dots but at the tone they represent.

Here's how: The Print Guide: Using a densitometer to measure plates

best, gordo

 

[RGPW17100]

I am trying to get a test sheet from prepress. We have to be out of the building we are in by April 15. I was hoping to get this figured out before then but sounds like we need to get production done so my press can be torn apart and moved. I hate to put this on the back burner but it could take awhile. I will post when I get some new information

 

[RGPW17100]

Prepress got me the test sheets and I printed them today. They have screen values from 5 percent to 95 percent for both conventional and specta. I only did the 40 percent as you mentioned. I forgot my densitometer and could not find the plate reader so the following links are only plate versus printed material. Stock was coated Flo with a gloss aqueous. Let me know if you need more.

http://home.comcast.net/~printergod2000/dotgainconventional.jpg

http://home.comcast.net/~printergod2000/Plategain copy.jpg