Ink Dating Expert Witness
|Contact our Ink Dating Expert Witness Lab Today!||Erich J. Speckin Forensic Document Analyst Ink Dating Specialist|
Ink Dating Expert Witness – Document and Handwriting Experts
Ink Dating is done in two primary forms. The first ink dating method is the static approach, which determines when the ink being examined was manufactured. The second ink dating method is the dynamic approach, this method is to determine when the writing occurred, or in simple terms, how long the ink has been on the paper.
The ink dating static approach is typically more useful as the difference between the date on the document and the present time increases. Several different tests exist in this form of ink dating. These ink dating methods include the comparison of the examined ink to a known library of standards, commonly called the library approach, the detection of chemical date tags placed in the ink purposefully by the manufacturer, commonly called the date tag method, and also the determination of the type of ink writing instrument used.
The determination of the type of writing instrument is probably the oldest method of ink dating. This ink dating method primarily involves microscopic examinations and can also incorporate some basic chemical solubility testing. Some examinations can be performed on fountain pens to determine type of nib, type of ink and the first date of introduction of each of these. However, since this is a very small portion of the actual type of cases seen, we will concentrate primarily on more recent developments.
Other pages discuss the use of infrared to discriminate the differences between inks that visually and microscopically look identical. The next step would be the most basic ink dating form of thin layer chromatography (TLC) testing to determine if two or more inks are the same or different formulations. In order to do this the following steps are taken:
- Extract the samples of ink to be tested from the document or surface upon which the ink was written. (If the ink is on paper, the typical method for removing these samples is by the use of a hypodermic needle with the end blunted and sharpened.) The use of an internal plunger will aid in expelling samples once they are “punched” from the paper. A backer should also be used; it should be made out of a material that will not allow any contamination into the removed ink sample. Common backer include self-healing cutting boards, filter paper, plain card stock or even glass.
- The samples that are taken from an area to be examined are then placed in a vial. For this type of comparison six plugs is sufficient if taken with the hypodermic needle. With experience, smaller sample sizes of one or two plugs can be used by modifying the amount of solvent used to extract the ink and the manner in which the ink is spotted. The plugs are taken one at a time and placed directly in the vial after being removed. The vial size used for testing of this nature is ½ dram; this is slightly larger around than the barrel of a common pen. The vials should also have a screw cap.
- Once the plugs are in each vial, the vial is tapped so that all the plugs are on the bottom and to one side. The vial is then placed in a rack that is slanted to keep the plugs and solvent that is added on the same side.
- A strong solvent is added to each vial to extract the ink from the paper or other medium. The most solvent for ballpoint inks is pyridine for non-ballpoint inks is ethanol and water mixed in a 1: 1 ratio. Other solvents can be used for either type of ink if desired as long as some or most of the ink is extracted from the samples. When this type of testing is conducted, for similarities and differences in inks 4 to 10 plugs are used in the analysis and the volume of strong solvent added is between 5 and 12 microliters.
- One the strong solvent is added to the vial, care is taken to ensure that the solvent is covering all the plugs in the bottom of the vial. The vial is then rotated to agitate the plugs and the solution. The instrument used to inject the solvent into the vial can range from a pipetteman to a GC syringe. The most important characteristic is the ability to adjust the volume dispensed.
- When the solvent is covering all the plugs, it is placed into the vial rack, which is slanted, so that the solvent stays in contact with the plugs. The vial is then capped ant the solvent is allowed to extract the ink. The extraction time varies with the solvent used; however 5 minutes is almost always sufficient for maximum extraction. Allowing extra extraction time in a strong solvent will not have any effect on the results.
- While the solvent is extracting a TLC plate should be secured. The best type of plate to case for this type of comparison is a glass backed HPTLC (High Performance Thin-Layer Chromatography) plate. This type of plate should be activated prior to use in this examination by heating in a laboratory oven for 30 minutes at 100 degree C. This activation drives the water from the plate and allows for better separation of the dyes and more accurate measurement and calculation of the relative intensities of the individual dye ratios. An activated plate must be cooled prior to applying the extracted into the surface. This can be accomplished by placing the plate on a desktop for about one minute.
- The extracting solvent and ink mixture is now ready to be spotted to the surface of the TLC plate. Before sampling and spotting the vial should be rotated several times to allow for mixing of the solution and ink. For the spotting process it is best to use a mechanical spotter to apply the solvent to the TLC plate. Also a small volume pipette allows for more concise spotting and better development of the plate by keeping the spot size small. The volumetric pipette of choice would be a 1-microliter size. As a relative measure of volume comparison, a drop of water that would drip from a facet would be approximately 50 microliters.
- Remove the cap from the vial and place the one-microliter volumetric pipette into the solution. Allow the pipette to completely fill. Remove the pipette from the vial, place the vial back into the rack and place the pipette into the holder of the mechanical spotter. NOTE: In many mechanical spotters the vial holder is removable and is used to hold the pipette when extracting the sample from the vial. If this is the case, after the pipette is full, the holder is placed with the pipette into the mechanical spotter.
- The entire one-microliter volume is spotted on the plate in a single application. The next sample can then be spotted in the same manner by using a new pipette. After a one-microliter sample has been spotted for all the samples to be analyzed, a second sample is than taken from each vial and spotted exactly on top of the first sample taken for the same vial. This is easily accomplished with use of a mechanical spotter by putting the holder back to the same setting used for the first spot made from each vial. The spots should be between ¾ inches to 1 inch from the bottom edge of the plate and spotted along the longer edge of the plate. Obviously, if the plate is square, then either edge will work fine. Each sample’s spots should be separated by about ½ inch to ¾ inch to avoid touching of the spots. (See illustration of the progression when spotting the plate)
- The process of spotting successive samples of solvent and ink on top of the previous one microliter is continued until all the solvent has been removed and spotted for each vial. At this point the vials and remaining plugs can be discarded. The plate now contains a mixture of ink and solvent on the surface. The plate is now dried in a laboratory oven for 50 minutes at 80 degrees C to remove all of the extracting solvent. Some solvents will be dried from the plate faster that others. The 50 minutes is enough time to dry the commonly used strong solvents from the plate. If it is known to be sufficient, a lesser time can be used to dry the solvent from the plate.
- While the plate is drying in the oven, the desired mobile phase solvent should be prepared. (See table of common solvent systems used for ink analysis). The most common mobile phase solvent system used is Solvent System I. The mixture is placed into a TLC chamber, which should be as small as reasonably possible to fit the TLC plate being used for the examination.
Ink dating – chemical tag: The detection of a chemical date tag can disclose the exact year that the ink being examined was manufactured. Other times the results will disclose a range of a few years as possibilities the ink could have been made. Based on the identification of formulation, which will be discussed next, it may be possible to exclude some of the possibilities and further narrow the range sometimes to only one year. Manufacturers used two types of chemical date tags in their ink formulations. Neither of these is currently being used. It should be noted that some ink manufacturers never placed any date tags in their inks. The idea of getting manufacturer’s voluntary cooperation to incorporate these tags with their existing formulations was developed in the late 1960’s at the Bureau of Alcohol, Tobacco, and Firearms. This was to further the identification of inks using the standard ink library approach. (To be covered further down this page). In 1969, Formulabs of Escondido, California inserted the first type of date tag in their ballpoint inks. This was a single tag was could be extracted with the ink, separated and analyzed with ultra-violet light. For this reason this type of tag is commonly referred to as a florescent date tag. This single tag was later expanded to four tags, A, B, C, & D. By the combination of the presence or absence of each tag either a specific year or a range of years could be established. The procedure most commonly used for the detection, isolation, and analysis of these date tags in ink dating is:
- Take a sample of ink from the ink line in question (7-10 plugs if using a needle plunger).
- Extract the ink from the plugs using a strong solvent (pyridine works best).
- Spot the entire amount of solvent and ink mixture on a HPTLC plate without fluorescent indicators. Care should be taken to keep the spot size as small and concentrated as possible to allow easier viewing of the tags, since the tags in the questioned ink can sometime be faint. Typically one microliter of solution spotted at a time will accomplish this, allowing about 2-5 minutes between one-microliter applications.
- Also spot a known sample containing all four date tags (A, B, C, and D) next to the questioned sample. The known sample can be in the form of a compilation of inks that contain date tags such that all tags will be present in the mixture (one ink containing tags A and C and another ink containing tags B and D). The other form can be an extract containing only tags obtained directly from the manufacturer, which can then be dissolved with pyridine and used to spot.
- Dry the spots in a laboratory oven at approximately 80* C until the solvent is evaporated. Thirty minutes is usually sufficient to dry completely.
- Allow the plate to cool to room temperature for a few minutes.
- Develop the plate in a tank using a special mobile phase solvent that will only move the date tags from the original spot up the TLC plate for approximately twelve minutes. The time can be slightly more or less, however it should be optimized to allow for the best separation of the date tags.
- After the plate has been run, remove from the solvent chamber and allow the plate to air dry in total darkness. Heat and light will cause the tags to dissipate and either be more difficult to view or in some cases not be seen.
- The plate is then viewed using ultra-violet light. Once the TLC plate is viewed, all four of the bands in the known standard should be visible under ultra-violet light and they should be separated so as to be easily distinguishable from one another. A comparison is then made between the sample or samples being analyzed to the known or control standard. The presence or absence of each tag in the questioned ink should be based on first whether any florescent compound is visible in the same area as the corresponding tag in the control standard.
The comparison between the known tag and the questioned ink being examined should focus on whether the florescent compounds are the same color in the known and questioned. No more than three of the four tags were ever used in a given year. These results should then be photographed using ultra-violet light and color film for presentation at a later time if required. Color slide film has been shown to work well, especially since a print can be made directly from a slide or used in a projector for presentation.
Ink dating 1970’s and 1980’s: In the 1970’s and 1980’s, several ink manufactures used rare earth metals as a method to tag inks as to their date of production. The detection of these tags is complicated and requires expensive and rare scientific equipment. The primary method of detection of these tags is called XREOF (X-ray excited optical fluorescence). Information on these tags is confidential and closely kept. This type of examination is very rarely to never used in actual casework currently.
Ink dating – Alternate Method: Another method for dating inks using thin layer chromatography exists. The ink library approach, as it is commonly referred to, comprises the other portion of the static approach to ink age determination. This involves the comparison of the questioned ink being examined to a known library of inks to determine the manufacturer and formula of the ink. Then by researching the library information or contacting the manufacturer an exact date of commercial availability can be established. This would be significant if the date the ink was first available is after the date the ink was purportedly written. The method by which questioned ink is compared to a standard reference ink library is as follows:
- Take the samples of the ink to be identified as previously discussed with a needle puncher.
- Extract the ink from the plugs using a strong solvent; pyridine works well with ballpoint inks and many non-ballpoint inks. Another solvent for non-ballpoint inks to use is ethanol and water mixed at a ratio of one to one. It is important to compare questioned samples to library samples that used the same solvents to extract the ink.
- Spot the questioned ink and solvent mixture on a low resolution TLC plate of the same type that the comparison library is kept on. The entire amount of solvent should be spotted on the plate. Again care should be taken to keep the spot size as small as possible to keep the bands concentrated for accurate comparisons. Ink comparisons should have two samples of each ink, one with a light spot and one with a concentrated spot. The reason is that in some cases the amount of ink available for examination may be limited.
- Once the sample is spotted, the plate should be dried in a laboratory oven at approximately 80* C for 30 minutes. When the plate is placed in the oven, care should be taken to not place the plastic backed plate on anything metal in the oven since this can cause warping or distortion of the plate that will affect the appearance of the resulting chromatogram.
- After the solvent is dried off, the plate should be allowed to cool for about one minute.
- The plate is then developed in the same mobile phase solvent system as the library standards. Our library is, as most are done, using Solvent System I. The plate is developed for approximately 12 minutes. The solvent front should travel approximately the same distance as in the library standards that the comparisons are being made to.
- The plate is then removed and the excess solvent is dried from the plate in the oven for approximately 20 minutes.
- The resulting chromatogram is then compared to the library standard chromatogram. The comparison is made between the dyes present, the color of each dye, the distance the dye travels from the origin, and the relative concentration of each dye component.
- A list of all possible matches is the created based on the above criteria. Too many samples should be run rather than too few many possible matches exist. In many instances it may be possible based on a library search and the training and experience of the examiner and most importantly the examiner’s familiarity with the reference library to quickly narrow the search to a few or even one possible ink. It has been suggested by Cantu and Brunelle that before an examiner is an expert in the identification of inks, one thousand inks should be compared and identified as part of the training. This may seem to be a large number at first glance, however with a large library of inks, significant knowledge and experience becomes extremely useful when applied to casework and also to expressing the significance of conclusions as to the uniqueness of individual dye components.
- Another TLC comparison is then made using the questioned sample of ink as well as all of the possible matches from the library search on the same plate. This comparison is made on a glass backed HPTLC which allows for the greatest discriminating power.
- The samples are then taken, extracted, spotted, dried, developed, and dried just as described previously. The comparison is again made between the dyes present, the color of each dye, the distance the dye travels from the origin, and the relative concentration of each dye component. Additionally, the shape of the dye, and an examination under UV light should also be conducted for additional information about possible matches or eliminations.
In the stage of final analysis, if all the possible matches are eliminated then no conclusion can be drawn other than that the ink does not match any of the standards in the library. This is another place where a large body of knowledge of running inks is significant, to evaluate differences that are attributable to differences in batches of inks and differences that lead to the conclusion of different formulations. The best way to establish the degree of differences that can be caused by different batches of the same formulation is to run many samples of the same ink that is known to be different batches. With inks available in common production this is much easier than with inks that are rare. Any differences that the examiner attributes to differences in batches when making an identification or elimination should be demonstrable in some manner.
If the questioned ink matches more than one of the possible library matches then any of the following may be used to further discriminate some or all of the possible matches from the questioned sample if necessary or desired:
- A second TLC examination using a different solvent system to develop the plate
- A densitometer to analyze the relative intensity of the individual dye components
- FTIR – Fourier Transform Infrared
- GC – Gas Chromatography
- HPLC – High Pressure Liquid Chromatography
- Or another suitable method for analyzing components of ink
If several matches exist at any point, an opinion can be expressed that the questioned ink is “to a reasonable degree of scientific certainty” one of the possible matches. The earliest date that the ink could have been available would then be the earliest date of introduction of all the possible matches.
If the universe of possible matches is at some point narrowed to one ink formulation, then an opinion can be expressed that the questioned ink matches the formulation from the library to the exclusion of all other formulations in the reference library. The size of the reference library of the laboratory conducting the examination is also highly important in the chances of success and also in determining the significance of a match. The only time that a library search will not result in one and only one match is if either the questioned ink is not found in the reference library (this is primarily due to the newness of the ink or the incompleteness of the reference library) or if several samples from different manufacturers are so similar that they cannot be discriminated from one another. The second option should not be confused with the same ink manufacturer producing the same ink formulation for several different ink companies, such as, Formulabs producing the same ink formulation for Parker and Cross blue ball point pens. Many other similar examples exist. It should also be noted that if extensive fading has occurred, the ink and paper have been burned or excessively heated, or the sample is somehow contaminated, i.e. tape, highlighter, magic marker, etc., a positive match may not be possible. Obviously, no library can ever be complete and no exact measure of completeness can be accurately stated, since the number of unknown and unseen inks cannot be stated. This is why when an identification is made the opinion is typically expressed “to a reasonable degree of scientific certainty” or “very probably” but an absolute positive statement cannot be made without some form of qualification. If more analysis is done or some unique component is present, then less of a qualification is necessary.
Keeping up with changes in formulations by manufacturers is also important. In recent years several manufacturers have made minor changes to popular formulations, which are evident in the above TLC examinations. One example is, in approximately 1995 Bic added an additional bold blue dye to their blue ballpoint formulation. If an ink being examined contains this newer formulation with the additional blue band it could not have been written until in or after 1995. Another example is the addition of a yellow dye to the black ballpoint formulation of Itoya. This addition was made sometime in 1996. There are also numerous other examples like the two mentioned.
Ink dating – cases: In the following real case examples, one can see the manner in which the three thin layer chromatography tests can be used to aid in examinations.
Ink dating – first case example: In the first example is a diary detailing racial harassment was produced as part of the evidence by the plaintiff. There were many entries throughout four books some involving these allegations and many that did not. There were 54 entries from the four-year’s diaries that were at issue. All of the entries that did concern the alleged harassment had been contaminated with a yellow highlighter so that a relative ink age determination (discussed in the next chapter) could not be performed. The unquestioned entries were examined first. These inks were all uncontaminated and showed to be written by a large variety of different writing instruments over the four-year period of the diaries. If the questioned entries were genuine and written on or about their purported dates they should exhibit approximately the same degree of randomness. However, in this case it was found that two ink formulations were used to write 53 of the 54 entries regarding the claim of racial harassment. One formulation was a blue ballpoint ink and the other was a reddish-brown ballpoint ink. This grouping encompassed 53 entries over the four-year period. Furthermore, the questioned inks matched in formulation to other inks contained in the diaries but was a different batch of ink than any unquestioned ink in any of the four years of writing that was submitted, but all the ink in the questioned entries are consistent with one another. Based on this evidence it was concluded that the entries were not written at many different times throughout the years, as purported by the author; but instead at all the same time or near the same time.
Ink dating – second case example – In example #2, two entries were questioned, one consisted of a single word “aneurysm” and the other consisted of several words “No False aneurysm found”. The doctor denied writing these entries. A handwriting examination was conducted on these words, which is detailed in an earlier chapter as well as a relative ink age comparison, which is in the next chapter. A thin layer chromatography examination was conducted on the two questioned entries and compared to the writings known to have been written by the doctor denying authorship, as well as several dozen comparison samples from other writers throughout the chart. It was found that the questioned portions were written with a pen that only matched writings known to have been done by the doctor that was denying authorship and was a different ink and different pen than any writing that was done elsewhere in the chart by any other writer in the dozens of entries that were used for comparison purposes. This evidence butriced the conclusion of authorship that was arrived at from the handwriting examination.
Ink dating – third case example – In the third example a day planner contained one questioned entry in a diary for the calendar year 1993. The entry was written with a blue ballpoint ink. There were many different types of ink used throughout the diary. There were approximately 25 other day’s entries in the diary that also contained a blue ballpoint ink formulation. A thin layer chromatography (TLC) test was conducted to compare the ink formulations used to write the questioned entry to the other unquestioned blue ballpoint inks used in the book. If similar ink was found elsewhere in the diary, a relative ink age comparison test could have been conducted to determine when the questioned entry was written. However, the results of the TLC test showed that the questioned ink was a different formulation than any other entry in the entire diary. This result alone is an indication that the questioned entry was not written contemporaneous with its purported date. A subsequent TLC test was done to identify the make and manufacturer of the ink used in the questioned entry in order to determine when this type of ink was first commercially available. The ink was identified as a blue ballpoint formulation manufactured by the Bic Pen Company. However, Bic did not produce pens with this type of ink in them until 1995 and later. The standard ink formulation used by Bic was changed in January 1995 and this entry was written with the new formulation. Therefore, the entry could not have been written in 1993 as purported by the author but had to have been written sometime in 1995 or later.
Ink dating – fourth case example – The fourth example was a portion of evidence in a case that contained a mountain of evidence showing that some engineering notebooks were added to and written after the fact. Some of the evidence in this case has been discussed, in previous chapters of this book. The ink involved in this portion of the case was found in a pocket day planner for the calendar year 1989. Several entries were being used to bolster the admissibility of evidence that was now “stolen” and only copies existed so that no forensic testing could be done on the originals. The entries in the day planner referenced the existence of the “stolen” notebooks in 1988 and 1989. The ink that was used to write the questioned entries was identified as manufactured by Formulabs, formula 926. A subsequent examination showed that the questioned ink did not contain a chemical date tag. Since most inks manufactured by Formulabs contained a chemical date tag until 1994, contact was made with the manufacturer to determine if this formulation could have ever been produced with out a date tag before 1994. The manufacturer stated that the first time this ink formulation was produced with out a date tag was 1994. Therefore, the questioned entries containing this type of ink could not have been written until 1994 or later. In this case, another expert disagreed with the identification of this ink. The opposing expert concluded the questioned ink was manufactured by Bic. The black ballpoint ink by Bic has been produced continuously since its introduction in 1979 and is still produced today.
The issue of the identification was one of many issues that were put in front of a California Federal Judge to decide upon. The judge reviewed both experts’ TLC plates showing each identification of the ink. The judge concluded in a written opinion that the Formulabs 926 ink “is identical to the subject samples, the Bic is not” and therefore the entries containing that ink could not have been written until at least 1994 or later. He further concluded that the other expert’s identification was incorrect. This is an example of how a presentation can be made to the court using TLC testing to demonstrate the basis for a conclusion of an ink identification.
The results of another TLC test were used by the prosecutor in a criminal trial in Michigan in 1999. This case was somewhat unique in the manner in which the evidence was collected and submitted. The issue was a hit-and-run in a parking lot. The suspects then allegedly took the victim’s purse that had a checkbook and a “silver Tiffany pen” among other items. A “silver Tiffany pen” was recovered at some point during the investigation by an investigating officer. A TLC examination was conducted comparing entries from the victim’s diary (provided by the victim’s family) and the ink that was in the seized pen. The TLC testing showed the formulation to be the same in the pen as in the examined entries from the diary. The diary entries also contained no chemical date tag, as did the ink of the pen. This was also significant since the ink was an ink manufactured by Formulabs, which put date tags in most of their inks during the time period the pen was purchased by the victim. No differences were found at any level of analysis between the ink contained in the diary and the ink in the seized pen. This evidence was used in the criminal trial linking one of the suspects to the victim.
Ink dating – case example: The last example was a receipt book containing a receipt that was purported to have been written in 1987. The ink on this receipt was examined using TLC testing and specifically for the detection of a chemical date tag. The ink showed the presence of a date tag and the tag was determined to have been inserted in inks only manufactured during the calendar year 1989. This means that the ink could not have been used to write a receipt in 1987. The receipt had to have been written in 1989 or later.
The second way to date inks is by how long the ink has been on the paper, this is a dynamic approach to ink dating that measures changes over time to the ink as it sits on paper. This is by the “dryness” level in the ink; the testing is commonly referred to as relative ink age testing or relative ink dating. The “dryness” level is not “dryness” in the strict sense of the word but a chemical dryness that is tested. The method, by which this “dryness” is tested, is as the word relative implies, to compare the questioned ink to one or more samples of ink of known date. The three methods of comparison that are used are one or more of the following: rate of extraction or R-ratios, extent of extraction or percent extraction, and third, dye ratios. Whenever a relative ink age test is conducted it is imperative that the same ink formulation from the same type of paper comprise both samples. If these two parameters were not met than any direct comparison of samples to determine age would be invalid.
The following is a procedure by which the three comparison methods are conducted.
- Small microplugs of ink were removed from each document using a hollow hypodermic needle with an internal plunger. After the sample was “punched out” it was put into a glass vial. This was done in the laboratory in Hong Kong. Upon examination in my office the plugs were separated into four vials containing 8 plugs each, 2 of the vials were accelerated aged and 2 were not.
- The samples, whose age was accelerated were then heated in a laboratory oven at 100 degrees Celsius for approximately 30 minutes uncapped and then allowed to cool.
- The cooled vials were placed in a rack next to the corresponding unheatedsamples for the relative ink age comparison tests. Since the artificially aged sample represents an ink that is approximately 3 years old, if a significant statistical difference is found between the aged and unaged samples, it is concluded that the ink is still in the drying process and most likely less than three years old.
Relative Ink Age Comparison Tests – Ink Dating
Three different ink dating methods were used to measure the relative dryness levels of the heated and unheated samples: R-ratios, Percent Extraction, and Dye-Ratios. The first ink dating method is the rate of extraction, which measures the rate at which the dyes in the ink are extracted into a weak solvent by taking samples at different time intervals. The second ink dating method is the percent of extraction which measures the ratio of the amount of ink that can be extracted in a weak solvent, compared to the total amount of ink on the paper which is extracted using strong solvent. The third is the Dye-Ratio, which measures the relative concentration of each dye to one another. These procedures have been used for over ten years. If at least one of these tests shows a significant statistical difference between the heated and unheated samples, it is concluded that the ink is still in the drying process.
The following ink dating procedure was used on the samples taken from the documents:
- Eight plugs were in each vial from the accelerated aging method above.
- 16 microliters of a weak solvent were injected into the vial and allowed to cover the ink dating samples. The weak solvent used in this case was n-butanol.
- The solution was then mixed by rotating the vial between the thumb and forefinger. The vial was then placed in a holder that holds the vial at a slight incline so as to keep the ink plugs in constant contact with the extracting solution.
- At three different time intervals a four microliter aliquot was taken from the vial and spotted on an activated HPTLC Merck plate (heated at 100 degrees Celsius for 30 minutes).
- Immediately before the sample was taken from the vial it is stirred by rotating the vial between the fingers.
- A sample at each time interval was taken with a 4 microliter volumetric micro-pipette and the vial placed back in the rack until the next sampling interval.
- The solution contained in the micropipette was then spotted on the plate.
- Each spot was applied to the plate approximately 2 cm apart from left to right.
- All of the vials were then placed into the oven at 80 degrees Celsius for 25 minutes to evaporate off the weak solvent. They were then removed and allowed to cool.
- Then 10 microliters of a strong solvent were added to each vial and allowed to extract the remaining ink in each sample for 15 minutes (the strong solvent used in this case was pyridine).
- Each vial was then rotated to stir the sample and 4 microliters were then spotted next to the corresponding weak solvent spots for that vial.
- The plate was then dried in the oven until the extracting solvents are totally evaporated from the plate.
Method for Obtaining Raw Data for the R-Ration and Percent Extraction – Ink Dating
- The first series of five spots were scanned using white light and the amount of absorption was measured using a computer driven video densitometer with automatic integration.
- This was done for all four samples of five spots each (2 samples are heated and 2 samples are unheated).
- Calculations were then made to normalize the curves by dividing each time interval’s absorbence by the absorbence for the final time interval. The rate of extraction curves for each sample were then plotted as normalized value vs. sampling time.
- To calculate percent extraction, the absorbence for given time was divided by the sum of the absorbence of the strong solvent spot and the absorbence of 3 minute spot. Percent extraction curves were plotted as percent extraction vs. sampling time.
Method for Dye Ratios – Ink Dating
- The plate is developed in solvent I for approximately 10 minutes or enough time to separate the individual dye bands of the ink.
- The plate is then dried in a laboratory oven at approximately 100 degrees Celcius for 30 minutes or until the solvent is completely evaporated.
- The plate is then scanned on the video densitometer to get the absorbance values for each dye band in order to perform the calculations as set forth below.
Ink Dating Calculations
The calculations for the rate of extraction for each sample were made by dividing each absorbence value by the final absorbence value. This makes the 3-minute extraction value 1.00 in all cases. This allows for a mass-independent evaluation of different samples.
The calculations for percent extraction for each sample were made by taking the absorbence for the desired time and dividing by the sum of the absorbence for the 3-minute weak solvent extraction and the strong solvent extraction.
The calculations for the dye ratios were done by dividing the results for each band by one another. For example in a case of three dyes, 1 would be divided by 2, 1 divided by three, and two divided by three. This would have three dye ratios.
The plate above is a high performance thin layer chromatography (HPTLC) silica gel plate demonstrates the variation in several samples of blue non-ball point inks. Two manufacturers’ with several different formulations are present (samples #1-11,16 and samples #12-15,17). Similarities are noted in samples #3, 6 and 16, as well as in samples #4 and 7 and samples # 15 and 17. These similarities are attributed to the similarities seen in a given manufacturer’s product formulations.
|Contact our Ink Dating Expert Witness Lab Today!||Erich J. Speckin Forensic Document Analyst Ink Dating Specialist|