density difference and color shades

[Green Printer]

I have seen this many times on different presses and the same press. Using the same paper different inks, measuring density especially on blacks why does a black on one press measuring 1.50 look blacker or darker than the same job measuring 1.75 on another press. I have also seen this with different fountains using the same ink. Why does the lower density black look blacker?

 

[kansasquaker]

The first thing to consider is the instrumentation taking the measurements. If you aren't using the same instrument, even the same patch will read differently on two devices. Moreover, if one or both of the instruments are poorly calibrated you can get wildly different results.

Then there's the 'look blacker' bit. The densitometer only measures reflected light. A reading of 1.75 means the target object reflects less light than an object that measures 1.5. Assuming the instrument is working properly, it is a fact that the first object is less luminous than the second. That may or may not agree with your subjective assessment of 'blacker'.

 

[Green Printer]

We used the same densitometer, plates, blankets and paper.

 

[Deleted member 16349]

The difference in appearance may be due to the fact that the densitometer uses a fixed geometry, such as 45 - 0 degrees. When looking at the sample with the eyes, even thought the lighting conditions might be correct, the direction of the light onto the sample and reflecting off it, might cause it to look different.

 

[Green Printer]

Green use a 25 to 50 power magnifier. Look at the solid patches. Which ink has the least amont of voids in the ink film.

 

[Green Printer]

Green use a 25 to 50 power magnifier. Look at the solid patches. Which ink has the least amont of voids in the ink film.

Using a 50 power magnifier I looked at both batches of black the 1.50 density and the 1.75 density.

I would have never guessed it but the 1.50 density patch did not have any voids in the ink film. The 1.75 patch was full of voids and white spaces between the ink. Yet the 1.50 patch looked darker or blacker than the 1.75 patch that was full of voids.

Can anybody explain this?

 

[gordo]

Using a 50 power magnifier I looked at both batches of black the 1.50 density and the 1.75 density.

I would have never guessed it but the 1.50 density patch did not have any voids in the ink film. The 1.75 patch was full of voids and white spaces between the ink. Yet the 1.50 patch looked darker or blacker than the 1.75 patch that was full of voids.

Can anybody explain this?

The voids are not relevant - your densitometer does not see the voids.

Context is important to visual perception but not to an instrument. So you might be seeing the effect of simultaneous contrast.

Or you might need the help of a professional who's often invoked in print-related issues

to cast out the problem.

 

[Deleted member 16349]

Using a 50 power magnifier I looked at both batches of black the 1.50 density and the 1.75 density.

I would have never guessed it but the 1.50 density patch did not have any voids in the ink film. The 1.75 patch was full of voids and white spaces between the ink. Yet the 1.50 patch looked darker or blacker than the 1.75 patch that was full of voids.

Can anybody explain this?

Very interesting. I am also surprised at the result. Of course there has to be a reason.

I would be interested in how you see the two blacks if you illuminate both of the samples with a single light sources at 45 degrees and look at it at 90 degrees.

Also, if you place the samples right next to each other, do they look different?

I hope you find the reason.

 

[Alois Senefelder]

Visual Variation


Gentlemen and Green Printer,


Hopefully this PDF will give you the answer you seek


Regards, Alois

 

[Devil Dog Dan]

Using a 50 power magnifier I looked at both batches of black the 1.50 density and the 1.75 density.

I would have never guessed it but the 1.50 density patch did not have any voids in the ink film. The 1.75 patch was full of voids and white spaces between the ink. Yet the 1.50 patch looked darker or blacker than the 1.75 patch that was full of voids.

Can anybody explain this?

The white voids are actually called a water mottle, reduce water to scum and slowy bring it up till its just clean. Shoudl help. Thats a huge issue with scanning Densitometers as well.... Pressman dont look at the print and the scanner says whoops we are light bring it up it scums Pressman say wooo gotta bring water up and waaalaaa the typical dog chasing his tail...

 

[shorty83]

Well one issue I see is that you mentioned you are using different inks. Inks vary A LOT from brand to brand or UV vs WB. Also, did you read the dot gains on the patches? If they are different try getting them the same. Reading density alone does no guarantee that the inks will look the same. There are a lot of variables other than density.

 

[Tim-Ellis]

Hello Green,

Are you using the same paper for both these jobs?

 

[D Ink Man]

The question I have is did you have the density differences using the same "lot" of paper with different inks. You opened in saying that it was with different inks. Different inks can and will certainly give you a different numerical density number, even with the same lot of paper. The lower density black numerical value in fact may look darker, jetter, and denser than the higher reading density print.

Why?

This is due to the particular characteristics of two inherently different ink formulae. Numerous factors come into play when you look at 2 different black offset inks, if you have the privilege of knowing this. Usually you don't because they are competitive products. This is where you might need D Ink Man to pay a visit. Some of the explanation can be given here. Two blacks can certainly and most times due have different carbon containing blacks which will have an effect on the visual density due to the jetness inherent to a particular carbon. The vehicle systems within the formulas have a profound effect also. The job of the well versed ink formulator is to utilize a good wetting vehicle system that enables the carbon black pigment to be completely wetted, and to surround the individual pigment aggregates. By doing so, this exhibits the best properties such as gloss, strength development and transfer capabilities to name a few in the finished ink product.. Also, the grinding median used to grind/wet the pigment is a huge part of the accomplishment. There are many ways to achieve this in the ink making process. Three roll mills set to the correct psi for dispersion and grind are one. Another would be a bead mill, that achieves the pigment wetting by a combination of time, rotary shear and temperature. The bead or ball size, as well as the condition of them are other critical factors in seeking a maximum, properly wetted pigment. This also applies to the other numerous pigments used in making printing inks.

So in summary yes, the phenomenon of densitometrics measured can be a reality in a dynamic sphere such as yours versus what we see with our eyes as simple human visuality. I will not include dry back in the discussion here, as this may only cloud the points. That is for another discussion.

Hope this provides some understanding.

D Ink Man

 

[gordo]

Re: D Ink Man's post...

Methinks the only ink characteristic, from a densitometry/eyeball point of view, in this thread that might account for what was outlined in the OP would be a possible hue difference between the two blacks. A densitometer doesn't "see" color - at least not the way the eye/brain does. All the rest, e.g. pigment grind, dispersion, wetting vehicles, etc are not relevant to the densitometer or eye/brain.

 

[D Ink Man]

Who am I to argue?

 

[ljgoldberg]

"We used the same densitometer, plates, blankets and paper. "

Gloss can have a strong effect on visual density. The automatic reaction of the viewer is to tilt the sample to avoid a specular reflection from a high-gloss sample.
A 0/45 densitometer will report a higher density from a high-gloss sample than from a matte sample, even if the pigment load, and all other ink-related parameters (except gloss) are the same.
I'm convinced a majority of the industry doesn't understand the function of polarization in a densitometer. It doesn't "make a wet sheet read as if dry", it "makes a dry sheet read as if wet".
This is done by eliminating the veiling glare produced by matte surfaces, producing higher densities. The geometry of 0/45 densitometers eliminates specular glare, so that doesn't need to be considered.

Is the gloss of the two samples comparable? Can you borrow a gloss meter to put some numbers to it?

Larry Goldberg
Beta Industries

 

[Deleted member 16349]

It doesn't "make a wet sheet read as if dry", it "makes a dry sheet read as if wet".
This is done by eliminating the veiling glare produced by matte surfaces, producing higher densities.

Hi Larry,

Just for clarification. I hope you mean that the higher density will be read due to the polarization used in the densitometer and not that the matt surface produces a higher density. The sentence might be understood in both ways.

A long time ago, I remember your explanation of dry back resulting in lower densities due to the "veil"effect on the surface of the dry print and so far, that explanation has been the best one I have heard. I repeat it often when the topic comes up.

 

[D Ink Man]

Yes, and this 'veil effect' will be dramatically influenced by the inherent properties of "THE INK" based on "THE INKS" characteristics as I tried to so preciously explain before a concise reply from the King.

If you notice, Mr. Goldberg in his reply did not mention INK. INK is the vehicle of printing and is the largest influencer of reproduction of print. PERIOD. Chicken salad or Chicken $h!t. What you want?

Step back for a moment and realize that "Printing" can be accomplished without a densitometer without plates, without blankets and without paper. If you need no plates you can go Indigo or the fantastical Landa which will also require no blankets. And you don't need paper to print. Understand?

But you do need ONE THING. Take a S.W.A.G. at what that one ingredient is.

THINK gentlemen. Not a sermon, just some thoughts.

D Ink Man

p.s. Can anyone figure out what S.W.A.G. is? May not really apply here, since I speak from experience and truthfulness to the best of my abilities.

 

[gordo]

"It [polarization] doesn't "make a wet sheet read as if dry", it "makes a dry sheet read as if wet".

Could you elaborate on this? For example, instrument polarization is typical in Europe and press sheet data used by the standards groups are measured dry, so what is the effect of a press operator using a polarized instrument at press where the press sheet is wet? Does the polarization make the wet sheet appear wetter or does it have no effect at all? Is the effect to make the measurements of a press sheet that has since dried correspond to the measurements taken when the sheet was wet?

 

[Bill W]

S.W.A.G. - scientific wild ass guess. Use it often in flexo profile smoothing