In color match system,” Match” program offers you the best possible color formulations based on least cost and least metamerism. One has to develop excellent database based on substrate – class of colorants – process combination ( Fig.1). .One has to make these variables ( substrate-dye- process ) as constants. One can achieve better results if these variables are controlled properly or understood perfectly. One can see the predicted formula along with quality of reflectance match. One can see from the output ( Fig.1) that predicted matches are categorized (coded) based on three signal dots ( Red ,Orange and Green) . Green dot indicates that dye- selection combination will not give any problem in matching. Orange code indicates that combination may have one or two incompatible dyes and red code indicates that formula predicted is having incompatible dyes and this formula may give problem in reproducing the shade time to time. These color traffic signals give warning to colorist in advance.One has to incorporate such type of strategy in formulation and correction program.
Figure 1: Prediction of a Recipe based on Substrate-Class of Colorant-Process
The purpose of any color system is to match any given color” Right First Time (RFT)”. This will certainly achieve the reduction in time of coloring proces. With good matching program, one can achieve good matching in Laboratory and will be successful in transferring the Lab formula to Production. One may face a problem when one transfers the established recipe to production. One will not be in a position to catch the color in first shot. Right First Time (RFT) is your dream as colorist and anyone would like to get the desired color in “zero shot”. That means you do not want to do any tinting further. It is a little difficult situation even though you have standardized colorants, you have assembled the batch accurately and you have controlled the coloring process minutely and accurately. In such situation, you have to correct the batch by using effective correction program. Sometimes, even in the Laboratory, you have to repeat the process of coloration for getting a perfect match. You have to have good correction program which considers all the parameters which affect the final color in production.
There are number of color software packages available in the market. Most of them offer good” Match” programs. You have to evaluate these color software packages for correction program module even though match and QC modules are working excellent. In any good color software package, color correction strategy used is the most important factor and decides the quality of color software. Logic used in correction program is shown below:
Logic Used in Correction Program : Iteration Method
I have worked on number of color software packages available in the market. During last few years, almost every color software company has offered new software versions after every three or four years. Each new version was refined and it was much better and something new or novel. However, it is very difficult to make comparison with each other as each one is using different color correction strategy.
It is my experience that most of the users of color system do not effectively use correction program and just use the system for match prediction and routine quality control of incoming or outgoing material. Most of them stop using correction module or get frustrated. This may be because correction program is not effective or they find it complicated.
In case of paint industry, color correction program is the most useful program for reducing tinting cycle .One has to get the required target shade in one or two add. They need correction program more often in production tinting. As you know, situation in production tinting is just like “Fire Fighting”. It is a regular event.
In case of textile dyeing, one has to avoid re-dyeing or stripping of the color. Color correction process is very expensive process and one has to achieve the target color” Right First Time”. This is a real challenge when number of process variables make it difficult.
In case of plastic coloration, once the coloration process is complete, you cannot do anything. You reach a situation of “point of no return”. Nothing can be done as we do in paints or textile application.
Generally, correction programs are designed for different purposes. I am listing some of the important features needed for color correction module.
1) Laboratory correction: Positive correction or negative correction. In this case, in Laboratory, you can re-dye or re-assemble the batch with a new corrected recipe. It is possible to correct with negative correction i.e. you can subtract the colorant amount. The dye which has gone in excess can be reduced in new corrected formula ( Fig.2). In paints and textile application it is useful.
Figure 2: Color Correction Program
2) Laboratory Correction (Only positive add): As you cannot subtract a colorant from the batch, you have to have only positive add. You can only add a colorant. It is called shading or tinting. This is mostly used in paint processing. In paint production or at Point of Sales facility , you need this program for getting a desired target if recommended formula does not work.
3) Production Correction: You cannot have negative correction. You have to correct the existing colored material without stripping. It is called small tinting or shading to achieve the desired tone.( See Fig.3) One can see the performance factor ( cf) of three dyes. Black has behaved 2% higher,Red has behaved 0.01 % weaker and Yellow has behaved 9 % stronger. In this case , yellow is a measure problem because of which batch has failed. You can also see Fig 4 which is a different case where performance factors are completely out of range indicating the incompatibility of colorants
Fig.3 : Production Batch Correction
Fig.4: Correction output with Performance Factors of Colorants – cf factors are our of range
4) Interactive Add: In this option, you will have interactive dialogue with correction program. You will present the Standard and batch. It will predict the difference and display all color parameters such L*, a*, b*. DE etc., You will look at these parameters and make your own guess and ask the program “What If ?“. That means you will ask the program to predict what will happen to batch if you add or subtract any colorant or colorants .That means, if you add any colorant, what will you achieve? You can suggest the amount of colorant and computer will do iteration and predict what will happen after using your suggestion. You can add one, two or three colorants simultaneously and it will predict DE for your guess. It is called “Colorist -Computer” Interaction. It is a powerful technique for any experienced colorist. If you are not an experienced colorist, you can also optimize the colorants and program offers you optimum solution.
5) Adding Fourth Colorant: One can also add fourth or fifth colorant and see whether it gives better correction. Sometime, you need minor or small shading for achieving the desired tone. This flexibility of adding a new colorant is good but may create problem of metamerism.( Fig.5) You can note that fourth colorant Yellow Oxide is added in the correction. One can select a colorant and try to fix the required color property such as redder/greener, yellower/bluer or lighter/darker by using “FIX “tabs such as L,a,b, C and h. One can also do “Manual” correction using manual tab. One can also “Zero” the colorant. You can look at L,a,b plot and see how color is moving towards standard color. One additional facility is given by which you can select the colorant and press “Fine,Medium or Coarse” buttons and do addition or subtraction of colorant. At the same time watch the L,a,b plot and see how you are reaching the target. This is very effective tool for correction of a batch.
Figure 5 : Add new colorant for tinting with different options
6) Manual Mode: In this program option, one can correct the formula by selecting manual mode (colorist – computer dialogue) by opting for fixing L*, a*, b*, C* and h* values. This is a useful option for fixing preferred chromatic value(Fig.5)
7) Hard correction: Hard Correction is ideal for lab or production correction when initial batch recipe is far from standard. ( Fig.6)
Figure 6: Different Correction Option : Hard,Soft,Super Soft, Optimize
8) Soft correction: Soft correction is used for those recipes, which are not far from given standard.
9) Super soft correction: Super soft correction is used for preferred tint.This is useful for whites and black.
10) Optimized correction: Optimized correction is based on mathematical automatic correction program, which uses least distance travel approach.
11) Performance Factor: This Correction Program gives performance factor of colorant in a combination. It computes performance factors of colorant by looking at concentrations of colorants in standard and batch. It indicates, what has gone wrong? Is colorant in combination behaving differently? That means, for example you have added 3 % of colorant, but program sees only 2.8% or 3.2% colorant. That may be due to incoming lot of colorant used in production is weaker or stronger in strength or it may be that in a process you have selected, colorant which is not diffusing well in textile application or dispersed well in paint application or colorant pick-up in combination is different ( Colorant -Colorant interaction ).It also indicates development of color yield in isolation or combination. One can easily determine the incompatibility of colorants. You can see from Fig.7 that correction factor compensates the formula. Output indicates that reflectance curves are not perfectly matched resulting into metamerism. ( DE is 1.2 for D65 and DE is 0.6 for A)
Figure 7: Correction Factor based on performance of colorant
12) Graphic Additions: In this correction program option, you can see L, a,b or L ,C, h graph with your tolerance circle. Standard and your batch are located on your graph along with three colorants in combination. You can graphically add or subtract colorants till you reach the tolerance limits . This is the most innovative correction program, I have ever seen. This is very useful program. You see standard and Batch on L, a, b or L, C, h plot along with three dyes and you can graphically add the component till you get very close match. This innovative and powerful program helps you to learn coloring.( Fig.5 )
Military Colors: Olive / Khaki colors
In Olive or Khaki shades, one has to always use correction program for getting desired tone. Generally, if you add the fourth dye for shading which results into metamerism. One should always use tri-chromatic combination and never add the fourth dye.
Many times mixture dyes are used such as oranges, browns, olive , blacks. Dyestuff manufacturers recommend many mixture dyes such as oranges, olives, browns etc., if you have three dyes in combination and in this combination, you have one or two mixture dyes, you will end-up with five or six dyes in combination, naturally it will result into metamerism. If you look at reflectance curves, you will notice more than 4 or five peaks and if reflectance curves are not perfectly matched that will result into metamerism. (DE for D65 and DE for A will be different).
It is observed that when you use two colorants of same hues such as orange and yellow or two blues of different tones, you face problem in correction as colorants are incompatible. This is mainly happening because of the use of two colorants of similar hues ( Two yellows or Yellow and Orange Dye). Problem of Khaki and Olive is quite complex. It may be because you are using two dyes of similar hues. One should not select such combinations where two colorants of similar hues are used.
Correction for Black and Grey
Black is not black. You may be looking for preferred tone such as redder black or greener black. You may have to tint it or shade it with a new tint colorant. Many colorant manufacturers offer black colorant which is generally a mixture dye – a combination of two or three colors. Ideally speaking, you can get a black from three pure red, blue and green colorants. One can always select a tri-chromatic combination. You will face minimum problem. Similar situation will arise in case of grey colors. Always obtain reflectance match and never add fourth colorant.
Correction of white is always a problem. Fluorescent Brightening Agents (FBA) are used for enhancing the whiteness of the material. One has to tint the material with FBA. Proper selection of FBA material and its accurate and optimum concentration is very critical. One should quantify and obtain its performance with with concentration as K- M theory is not very effective for FBA.
TIPS for correction program
You must remember that color correction program is not effective because of reasons given below:
( I am giving listing for textile application.Similar problems can be listed in paints application and plastic coloration)
1) K-M theory is based on linear relationship of dye absorption and concentrations. Some of the dyes do not behave linearly. When one looks at the curve of (K/S) Vs. Concentration, one can find the change of low slope at low concentrations and high concentrations (<1% & >2%). Such behavior brings inaccuracy in match prediction and correction.( See Fig.8). You can look at colorimetric data of Blue colorant. Ideally speaking ,strength per unit concentration should not change. It is changing considerably indicating that dye stength is not linear. The slope curve of log K/S Vs Log C also indicates that it is changing.
Figure 8 : Reflectance data of Blue Colorant with Different Concentration
K/S Vs Concentrations
K/S per Unit Concentration
2) Recipe calculation is based on primary dyeing, using several different concentrations of selected dyes. If primary dyeing data is not proper, you will face problem in correction as same data is used for correction strategy.) The accuracy of primary calibration data determines the quality of the color correction.
3) One has to have highly accurate and repeatable dyeing. This is mainly experimental error if dye behavior is not linear.
4) In most cases when recipes are dyed under different conditions or on different substrate than primary dyeing, unacceptable color differences are obtained. Substrate correction factor is related to dye pick-up of substrate or pre and post treatment of substrate, which is used for dyeing. A simple substrate correction factor based on strength of dye will exist or statistical correction factors are to be obtained for each substrate.
5) Traditional color recipe calculations assume that dyestuffs, when mixed, behave the same way as used in isolation. Interactions between dyestuffs are not taken into account and lead to inaccurate color recipe.Dye strength/concentration relation may be linear, when dye is used in isolation. As soon as dye is used in combination (with one or more dyes), dye strength/concentration relationship is dramatically changed and many times not predictable. In such cases, one has to study the dyestuff behavior both in isolation and in combination and determine the statistical behavior for determining the perfect correlation factor.
6) Dyestuff behavior is based on dye-fiber interaction and dye-dye interaction. By keeping substrate constant one can find the correlation factor and apply the same for refining the prediction of the recipe.
7) Lab and Production correlations are related to process parameters and one has to obtain correct correlation factor. This can be established by collecting statistical data of lab and production recipes. The systematic analysis of final production recipe and initial lab recipe is carried out by using colorimetric data.
8) Effect of process parameters such as dye/ liquor ratio, pH, time-temperature, speed of operation etc., are to be determined and quantified for process standardization.
9) Standardization of dyes (Strength and chromaticity quantification) and proper selection of dyes for a given hue is to be done based on tri-chromatic combination.
Color correction program is the important tool for any colorist and considerable savings can be obtained by effective use of this program if proper correction strategy is used.
Dr Narendra S Gangakhedkar