color negative base

[L K Keerthi Basu]

hi friends,

 

can any one explain me why the color negative films are amber in color and why they differ to each other base density? Also tell me is there anystocks which have same base density.

What will happen If the actual base density of a particular stock become more dense.What is the base color of a dupe negative? Why the base color of positive stock is colorless or transparent. And why the amber color of the negative base is not reproduced in the positive.

[Dominic Case]

The base of colour negative films is clear. The amber colour that you see is in the emulsion itself.

 

The yellow, magenta and cyan dyes that are formed when film is exposed and processed are not ideal or pure colours. For example, the magenta dye absorbs green light as intended, but absorbs a little blue light as well, making it a bit too yellow.

 

So the emulsion is constructed so that unexposed areas of the magenta layer have a yellow colour (from the unexposed colour coupler). In exposed areas, the coupler is converted to magenta dye, so that this original yellow colour is removed - but is replaced by the unwanted yellow cast of the magenta dye. The end result is that the entire image has a yellow cast to it, whether it's from the unexposed coupler or the exposed and developed magenta dye.

 

Same goes for the cyan dye, which absorbs a little green and blue light as well as red: the coupler is a slightly red colour to start with, and so abosrbs the same amount of green and blue as the unwanted absorbtion of the cyan dye.

 

The red and yellow couplers together add up to the amber colour you see.

 

The positive print stock is balanced to compensate for this amber bias, being slightly more sensitive to blue light and less to red light. Printing from a neutrally-coloured negastive (such as a b/w neg) would result in a very cyan-blue positive image.

[L K Keerthi Basu]

The base of colour negative films is clear. The amber colour that you see is in the emulsion itself.

 

The yellow, magenta and cyan dyes that are formed when film is exposed and processed are not ideal or pure colours. For example, the magenta dye absorbs green light as intended, but absorbs a little blue light as well, making it a bit too yellow.

 

So the emulsion is constructed so that unexposed areas of the magenta layer have a yellow colour (from the unexposed colour coupler). In exposed areas, the coupler is converted to magenta dye, so that this original yellow colour is removed - but is replaced by the unwanted yellow cast of the magenta dye.  The end result is that the entire image has a yellow cast to it, whether it's from the unexposed coupler or the exposed and developed magenta dye.

 

Same goes for the cyan dye, which absorbs a little green and blue light as well as red: the coupler is a slightly red colour to start with, and so abosrbs the same amount of green and blue as the unwanted absorbtion of the cyan dye.

 

The red and yellow couplers together add up to the amber colour you see.

 

The positive print stock is balanced to compensate for this amber bias, being slightly more sensitive to blue light and less to red light. Printing from a neutrally-coloured negastive (such as a b/w neg) would result in a very cyan-blue positive image.

<{POST_SNAPBACK}>

 

then why any two negatives don't have the same base density. This happens because of what? What is the actual color of the magenta color coupler and cyan color coupler?

 

according to the reply to my PM Mr.Dominic you said that the Yellow filters are water soluable dye but I read in a book it qoutes that the Yellow Filter is made out of arrangement of fine silver halides, so that these silver halides will absorb all the blue light and sends only the green and red light. These silver halides are soluable in fixer because that it had crossed the bleach solution.

I thought what I read may be wrong so that I have asked you, I have little bit confused with these two type of answers.

 

thank you,

 

l.k.keerthi basu

Edited January 10, 2005 by l.k.keerthibasu

[John Pytlak RIP]

Each color negative film is optimized for performance, and may use slightly different formulations of colored couplers, so the D-min (minimum density) may vary with the film type and film manufacturer.

 

Kodak (Ralph Evans) developed the technology of colored coupler masking in the mid 1940's for Kodacolor film, and later EASTMAN Color Negative film. It was the first of many developments that enabled the excellent color reproduction of Kodak color negative films today. :)

[John Sprung]

it qoutes that the Yellow Filter is made out of arrangement of fine silver halides, so that these silver halides will absorb all the blue light and sends only the green and red light.

<{POST_SNAPBACK}>

Silver halides, filters, and dye couplers are three different things.

 

Silver halides are sensitive to blue light. Their sensitivity can be extended into the green by adding other chemicals, which is what made orthochromatic B&W film possible. Later, still more additives extended their sensitivity all the way to red, making panchromatic B&W.

 

In color film, there are three layers containing the light sensitive silver halide grains, and between them there are colored filter layers to block out the colors that have been recorded in the upper layers from contaminating the lower layers. These filter layers are only needed during exposure, and I'm pretty sure that they get completely washed away in processing. They're just colored dyes, not much different from the ones in gelatin filters you might put in front of the lens.

 

The halide grains are attached to dye couplers, which make one color if they're attached to an exposed grain, and a different color if the grain is not exposed. You could have them make a color for exposed grains and clear for unexposed, but it turns out that another color works better than leaving the unexposed areas clear.

 

The reason is that due to some deep physics of chemical bonds, the dyes that are possible to make in the real world give you a nice sharp cutoff for the warm colors like red and orange, but in the greens and blues, the curves are nowhere near as steep. A red dye lets thru a lot of red, and very little blue and green. A blue dye lets thru more blue than red or green, but it cuts out a lot more blue than you would like, and lets thru more red and green than you would want.

 

By leaving orange and yellow behind instead of clear, the film "borrows" some of the nice filter characteristics of the warm colors to improve the purity of the cool colors. Bottom line, the orange stuff helps the film do a better job of sorting photons out into red, green, and blue.

 

 

 

 

-- J.S.

Edited January 10, 2005 by John Sprung

[Phil Rhodes]

Hi,

 

It's not even always orange - they've got all this intermediate stuff at Filmlight, and it's pink.

 

Phil

[Dominic Case]

according to the reply to my PM Mr.Dominic you said that the Yellow filters are water soluable dye but I read in a book it qoutes that the Yellow Filter is made out of arrangement of fine silver halides,

For many years the yellow filter layer was indeed made of silver: it was known (but probably not widely) as the Kary Leigh layer. By choosing the exact particle size it was possible to make the silver absorb blue light and pass red and green onto the emulsion layers underneath.. However it also reflects and scatters light, so the silver has been replaced by a yellow dye in modern emulsions. I've no idea when this was changed - John Pytlak may know, and may also tell us about Mr Kary Leigh ??

 

then why any two negatives don't have the same base density.

(we're back onto the integral masking now)

Once again, the orange colour is NOT the base. The base is clear. The orange colour you see is in the emulsion, and is due to:-

1. integral masking, as described previously. Different emulsion types may have different advances in technology in them. Purer dyes need less correction, and therefore different amounts of masking. Different manufacturers may choose different chemicals to do a similar job.

2. d-min. This is the trace amount of developed image in unexposed areas, and is due to age, heat, radiation, and the natural activity of the developer. Older emulsions (especially high speed ones) will tend to have a slightly higher d-min. Different emulsion layers may be affected differently, resulting in - for example - more increase in the blue d-min, and a yellower colour to the film.

[John Pytlak RIP]

Dominic Case asked:

 

I've no idea when this was changed - John Pytlak may know, and may also tell us about Mr Kary Leigh ??

 

 

The yellow filter layer can contain colloidal silver that absorbs blue light, known as Carey Lea Silver (CLS):

 

http://www.freepatentsonline.com/5360703.html

 

In the photographic element a yellow filter layer is provided between the slow yellow and the fast magenta. This layer can comprise Carey Lea silver (CLS), bleach accelerating silver salts, any oxidized developer scavenger known in the photographic art, such as described in U.S. Pat. No. 4,923,787, and a dye to enable improved image sharpness or to tailor photographic sensitivity of the element. A preferred oxidized developer scavenger is: ##STR10##

 

Other oxidized developer scavenger useful in the invention include: ##STR11##

 

When finely divided silver such as Carey Lea silver is used in the yellow filter layer, and when a bleach accelerating releasing coupler (BARC) is present in the photographic element, then preferably an interlayer is provided between the yellow filter and other layers in the photographic element containing a dye image forming coupler.

 

http://patdb.ffii.org/EP/6/8/EP689092.html

 

Development accelerators can also include such things as competitors for oxidized developer, as described in, for example U.S. Patent 4,923,787; and the incorporation of fine grain silver halide crystals (e.g. Lippmann), or fine grain silver (e.g. Carey Lea Silver), or surface or internally fogged silver halide grains, into an emulsion layer, as exemplified in U.S. Patents 4,656,122, 4,082,553, 2,996,382, 3,178,282, 3,397,987, and 4,626,498.

 

More about Carey Lea:

 

http://www.sas.org/E-Bulletin/2003-10-31/chem/body.html

 

Colloidal silver was investigated by the 19th century American chemist, Matthew Carey Lea (1823-1897), an inventor of photographic processes. Here are some of the recipes for preparing "Carey Lea's silver":

 

Silver hydrosol (by reduction with ferrous citrate)10

 

Prepare the following solutions:

 

Silver nitrate (10%): Dissolve 1.1 g AgNO3 in 10 mL distilled or deionized water.

 

Ferrous sulfate (30%): Dissolve 4.3 g FeSO4.7H2O in 10 mL distilled or deionized water.

 

Sodium citrate (40%): Dissolve 6.6 g Na3C6H5O7.2H2O in 10 mL distilled or deionized water.

 

Combine the latter two solutions, neutralize to litmus with a few drops of conc. sodium hydroxide and quickly add it to the silver nitrate solution.  Mendeleeff stated that a lilac-colored precipitate will be thrown down and subsequently turn blue.  In my experience the mixture immediately turned dark blue, almost black, and part of the solution came down as a dark blue precipitate, with some remaining in colloidal suspension.  On filtering the suspended silver passed through the filter while the precipitated silver was retained.  Wash the precipitate on the filter with ammonium nitrate solution (7 g in 100 mL distilled or deionized water).  Note that little or none of the precipitate dissolves to pass through the filter.  Here the ammonium cation acts to neutralize the charge on the silver micelles thus inhibiting their dispersion.  However the precipitated colloidal silver is "reversible", that is it can be dispersed by removing the neutralizing cations.  Wash the precipitate on the filter with distilled or deionized water. The silver will now disperse in the water and pass through the filter.  The resulting silver hydrosol may present a color ranging from bright red to a very deep

red-brown

 

This property of reversibility can be employed to purify the sol from the salts used in its preparation.  Reprecipitate it by adding a saturated ammonium nitrate solution (12 g in 10 mL water.  Decant off the supernatant liquid and wash the precipitate with two or three small quantities of 7% ammonium nitrate.  Disperse the washed precipitate in 100 mL distilled or deionized water.  The resulting silver hydrosol is bright red by transmitted light and chocolate brown by reflected light.  This process can be repeated for further purification if desired.

 

As noted above, ammonium (and other monovalent cations) yield precipitates that are reversible.  Divalent cations likewise precipitate hydrosols, but the effect of the double charge is not twice but many times that of the monovalent NH4+.  Add a few drops of calcium chloride solution to silver hydrosol in a test tube.  The resulting precipitate is irreversible and will not redisperse on washing with water.

 

http://www.imaging.org/store/epub.cfm?abstrid=196

 

The latent image formed by exposure was found to be at least partially resistant to attack by nitric acid and this led Eder and Carey Lea to introduce the sub-halide theory of the latent image in 1886 and 1887. This theory dominated discussion of the formation and properties of the latent image until 1899 when it was challenged by Abegg and Schaum who revived the silver nucleus theory. Lüppo-Cramer and Reinders demonstrated in 1909 and 1911 that the sub-halides which had been studied by Carey Lea were formed by distributions of colloidal silver within the silver bromide.

 

http://32.1911encyclopedia.org/S/SI/SILVER.htm

 

Colloidal silver is the name given by Carey Lea to the precipitates obtained by adding reducing solutions, such as ferrous sulphate, tartrates, citrates, tannin, &c., or to silver solutions. They dissolve in water to form solutions, which do not penetrate parchment membranes, hence the name colloidal.

[Dominic Case]

John Pytlak may know, and may also tell us about Mr Kary Leigh ??

You haven't disappointed us, John! More about Kary Leigh and his colloids than I though possible!

 

Notes from a Kodak training program on the construction of colour film stocks:-

 

Then the blue sensitive layer is positioned on top. 

. . . a yellow filter layer is positioned underneath the blue . . . .

The next most sensitive layer is the green sensitive layer and then the red is on the bottom.  . . . . For years this layer was called Kary Leigh Silver Layer.  Very fine silver was put there. . . .  Modern films do not use silver because silver can defract light.  So a  yellow dye is put  there, and almost all modern films have that.

 

As Phil points out, intermediate stocks (5242, 2242) as used for making IPs, dupe negs and digital negs from laser recorders) aren't so much orange as pink - absorbing less blue light than most camera emulsions (presumably the dyes are different).

[John Pytlak RIP]

Thanks, Dominic.

 

I'm not always privy to the exact formulation used for each film, but I do know that they are optimized for the intended use, bearing in mind the need to have all the films work together, especially when intercut into the same roll. So although the D-min color may vary, the films generally have the characteristic orange-pink color of the colored couplers, and can normally be printed together.

 

As you note, either dyes or Carey Lea Silver may be used as a filter to minimize the affect of blue light on the red and green sensitive layers. Of course, either is removed from the film during processing.

[L K Keerthi Basu]

thanks John and Dominic,

 

Now Iam clear with my doubts. Why the green sensitive layer was placed on the top in the Positive emulsion? Is there any particular reason about placing this on top.

May I know what type of dyes they use for negative and positives , paritcularly in Eastman. What is the scentific name for each dye which is used.

 

Really how many layers are there in a negative and a positive film, I don't know but I think that it must exceed above 10.

Edited January 11, 2005 by l.k.keerthibasu

[John Pytlak RIP]

thanks John and Dominic,

 

  Now Iam clear with my doubts.  Why the green sensitive layer was placed on the top in the Positive emulsion? Is there any particular reason about placing this on top.

  May I know what type of dyes they use for negative and positives , particularly in Eastman. What is the scentific name for each dye which is used.

 

  Really how many layers are there in a negative and a positive film, I don't know but  I think that it must exceed above 10.

<{POST_SNAPBACK}>

 

Motion picture color print film is printed from orange-masked color negatives on a printer that uses a low color temperature tungsten lamp. So the blue sensitive layer needs to be considerably faster than the green and red sensitive layers (unlike a color camera film). Since the green and red sensitive layers are so much slower than the blue sensitive layer, there is no need to filter out the smaller amount of blue light from the "native" sensitivities of the red and green sensitive layers. Although a UV-absorbing filter like a Wratten 2B is used in the printer setup.

 

About 60% of our visual information is from the green portion of the spectrum, 30% from the red, and only 10% from the blue. So in print film, it makes sense to put the green (magenta) imaging layer on top, to maximize sharpness. The relatively fast and grainy blue (yellow dye forming) layer can be at the bottom of the pack, since it is least important to the sharpness and granularity of the final image.

 

The specific formulations of film emulsions are considered proprietary information, as are the details of the film emulsion coating process. The classes of dye-forming couplers used are discussed in the patent literature, and in publications such as "The Theory of the Photographic Process" by T. H. James, Macmillan Publishing Company, ISBN 0-02-360190-6.

 

Kodak publication H-1 is an excellent introduction to Motion Picture Film technology:

 

http://www.kodak.com/country/US/en/motion/.../h1/index.shtml

 

The Kodak Motion Picture Processing manuals also have a very good discussion of film structure and processing chemistry (especially Modules 7 and 9):

 

http://www.kodak.com/US/en/motion/support/....4.5.16.8&lc=en

 

 

The KODAK Motion Imaging Workshop provides a fundamental understanding of film technology and associated processes, with recommendations for practices and procedures to obtain optimum image quality:

 

http://www.kodak.com/US/en/motion/support/...1.4.9.4.6&lc=en

 

Purpose

 

The KODAK Motion Imaging Workshop provides a fundamental understanding of film technology and associated processes, with recommendations for practices and procedures to obtain optimum image quality.

 

Benefits

 

Program modules can be delivered individually or combined into a comprehensive 2 - 3 day workshop. Advantageous for lab personnel, cinematographers, and film students.

 

Topics Include

 

Color Theory

How Film Works

Film Formats

Image Chain

Origination, Intermediate, and Print Films

Process ECN-2, ECP-2B

Process Control

Turbulation

Printing and Timing

Film Sound

Positive Ways to Handle Negatives

EASTMAN KEYKODE Numbers

Film in Post Production

Alternate Processes

Ordering Information

 

Contact your local Customer Service Representative or Kodak office for price and availability in your area.

 

For workshop availability contact the Customer Training Department:

us-ei-Training@kodak.com.