September, 1933
IKDUSTRIAL AND ENGIXEERING CHEMISTRY
1033
25, 48 (193.3). ( 5 ) Ladenburg, A , , Ber., 9, 1524 (1876). (6) Phillips, M., J . Am. Chem. Sot., 49,474 (1927). Schol' and K a c e r g Ber.i 37v 4533 (lQo4). (8) Senn, E., Dissertation, Z u r i c h , 1923. 1.9) Tanaka, M., and Tanaka, S . . Bull. C'hem. SOC.Japan, 3, 286 11928). ~--,(4) Groggins and Stirton, Ibid.,
..~CKSOWLEDGMENT
The equipment shown in Figure 1 was designed and constructed by R. Hellbach of the Color and Farm Waste Division of this bureau.
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LITERATURE CITED
RECEIVED March 24, 1933. Presented before t h e Division of Dye Chemistry a t t h e 85th Meeting of the .Imerican Chemical Society, Washington, D. C., March 26 t o 31, 1933. This paper is Contribution 221 from the Color and F a r m Waste Division, Bureau of Chemistry and Soils.
\l) Bayer, A., German Patent 170,562 (1904). (2) Bayer, A., German Patent 178,130 (1905). '3) C'arsn-ell, T . S., ISD ENG.Cmxr., 20, 728 (192S'i.
Colored Waterproof Drawing Inks ELMER R. ZIMMERM4
~ Bureau ,
of Standards, Washington, D. C.
T
A method f o r preparing a set of water-fast made, using a b o u t 100 ml. of drawing inks is described. The inks consist of a ments described was to the m i x e d e t h e r s each time. p r e p a r e a n u m b e r of After the last e x t r a c t i o n the 5 per cent solution of shellac and a suitable dye. representative clear water-fast shellac solution heated on inks of the dissolved dye type The is in so1ution ammonium hythe steam bath for 2 hours in which would not deteriorate on droxide and a small amount of borax. Seaen order to eliminate all traces of dyes. each of a diferent color. selected from a list the ethers. The shellac content storage over a period of a t least "" one year. of ninety-two as the most suitable f o r making the was The chief constituents of a determined, 5 ml. of a m m o water-fast inks, are listed. .Vethods of testing water-fast ink are shellac and a nium hydroxide were added to s u i t a b l e dve. The shellac is wafer-fast inks are outlined. insure an excess of this conheld in an aiueous solution with stituent, and the solution was dia weak base or an alkaline salt, such as borax. I n an ink luted with water until the shellac content was reduced to made by the procedure outlined later, ammonium hydroxide 50 grams in 500 ml. One gram of phenol and 3 grams of is depended upon to keep the shellac in solution. However, a borax were added, and the solution was vigorously shaken small amount of borax is necessary to make the shellac in- until these materials were dissolved. soluble when the ink dries. I n the course of this work it The stock solution thus prepared was used in making the was found that unbleached shellac could be used because the samples of ink. Convenient batches of the ink were made by amount of natural dye in the shellac is not great enough to mixing 50 ml. of the stock solution with 50 ml. of an aqueous alter the shade or hue of the finished ink. Consequently no solution of the dye. The ink was then filtered to remove any attempt was made to use bleached shellac in the work here insoluble material introduced by the dye. described. The impuiities, such as insoluble waxes, orpiThBLE I. DYESSUITABLE FOR COLORED WATERPROOF nient, and dirt, were removed from the orange shellac. DRAWING INK Apparently the more important of the two constituents is D Y EI N the dye. Of ninety-two dyes tried, only seventeen were of CoLorn 100 ML. sufficient promise to justify using them in inks to be kept in INDEX SCHULTZ O F DYE CoLon No. No. INK storage for a year or more. The other seventy-five dyes were Gram unsatisfactory because they were not soluble enough, they Erythrosine Yelloaish Red 772 591 0.5 Oranee R Oranee 7. .8 70 n 6 did not produce a water-fast ink, or their color lacked the Brilliant Chloramine Yellow Yell&: 814 617 0.4 desired purity. At t,he end of a year, seven of these dyes Brilliant Milling Green B Green 667 503 1.2 Blue G E x t r a Blue 736 565 0.5 representing different colors were selected as the best for Wool Methyl Violet B Violet 680 515 0.5 Brown 596 476 0.8 making water-fast drawing inks. Inks prepared with these Benzamine Brown 3 G 0 seven dyes did not change color or deteriorate in any way CHOSEN FOR P R E L I M I N A R Y SAMPLES O F I N K during the aging period. At the end of two years, these TABLE11. DYES BUT ELIMINATED IK FINAL SELECTIOX inks were htill good. They bled very little, if any, when subD Y EI S jected to the most drastic water-fastness test both before and COLOUR 100 M L INDEX SCFIULTZ OF after aging. The dyes which were found to be suitable for DYE COLOR No. No. INK the preparation of colored water-fast inks are given in Tables Cl'ram Benzo Fast Orange S Red 326 279 I and 11. HE object of the experi-
Y
.
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PREPARATION OF A WATER-FAST I m A shellac solution was prepared by carefully digesting on a steam bath about 65 grams of orange shellac in 500 ml. of a solution containing one volume of ammonium hydroxide (qpecific gravity 0.90) mixed with 4 volumes of water. When the shellac had completely dissolved, the solution was allowed to cool. The waxes present were removed by repeated extraction with a mixture of equal volumes of ethyl ether and petroleum ether. Each extraction required about 3 hours to obtain a complete separation. Four such extractions were
Benzo F a s t Orange S Brilliant Croceine hZ Orange R Thiazol Yellow Metanil Yellow New Methylene Blue N Crystal Violet Benzo Brown G
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Red Orange Yellou. Yellow Blue Violet Brown
{ 2161 "; 813 138 927 681 606
279 227 151 198 134 663 516 485
The seven dyes of the first choice, each of a different color, together with the quantities necessary for the preparation of the batches of ink are given in Table I. The dyes listed in Table I1 are of second choice. Inks prepared with these dyes are not quite as fast to water as those in Table I. I n preparing any of thepe ink., the concentrated form of the dye
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I N D U S T R I A L A N D E N G I NE E H I N G C H E M I S T R Y
is desirable to prevent introducing unnecessary materials into the inks. The figures in the tables indicating the amount of dye used are only approximate because different manufacturers may furnish dyes that are identical except for their tinctorial power. At the end of two years, all of the inks in both tables were in good condition except one of the bottles of violet ink containing crystal violet. A heavy growth of mold had destroyed the color of this sample, but the other sample containing the same ink was not affected.
METHODS OF TESTIKG hfethods of testing water-fast inks were developed as the work progressed. At first, lines were drawn with a ruling pen on bond paper and allowed to dry for 2 or 3 hours before they were immersed in tap water for 15 minutes. As better inks were prepared, a more drastic test became necessary. This latter consisted in placing the paper, marked with the ink to be tested, between pieces of glass held in running water.
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As soon as the paper was in place, the two pieces of glass were pressed together to remove excess water and set aside for one hour. If the dye bled, it discolored the paper adjacent to the streaks, and the amount of bleeding was judged by the area of paper discolored. To supplement this test, strips of the paper were soaked for one hour in 200 ml. of water which was stirred occasionally. The amount of bleeding was determined by the decrease in the intensity of color of the streaks. This test was not as sensitive as the one in which glass plates JTere used, but it showed whether or not the bleeding noticeably affected the intensity of color. The most drastic test was made by marking a dry paper strip with the ink to be tested, covering with a moistened filter paper, and placing the two between dry glass plates. Any dye that bled from the streak was absorbed by the filter paper. This test is a very convenient one for judging the relative merits of two or more inks. RECEIVED March 7, 1933. Published by permission of the Director, Kational Bureau of Standards.
Blue Dye as Evidence of the Age of Writing C. E. WATERS,Bureau of Standards, Washington, D. C. Contrary to statements made by experts on those [ c h e c k s ] w r i t t e n five ItDINARY b l u e - b l a c k disputed documents that the blue dye in writing years; while a f t e r six y e a r s writing ink is essentially an aqueous solution cont h e reaction became very t a i n i n g ferrous sulfate, tannic with Ordinary ink be slow and there w e r e h a r d l y and gallic acids from nutgalls, oxidized away in 15 Years, examination Of 147 any signs of diffusion of the samples of writing older than 15 years showed blue pigment. On the checks free mineral acid to delay the that blue dye was to be f o u n d in 78 of them. twelve years old the ink was deposition of ferric gallotannate detected unaffected for a long period by as the ink oxidizes, and an antiThe oldest samples in which dye t h e r e a g e n t . ” And on the septic. Freshly made ink of this were written in 1881. following page: “In abnormal kind makes such pale marks on paper that it is customary to add It is not Possible to conclude .from the Presence c a s e s , w h e r e an e x c e s s i v e or absence of dye that one sample of writing is amount of ink had been used, also a dye, usually blue, to give some diffusion of the blue pigan immediate color. On paper, more recent or older than another. ment may occur even after the the writing is a t first blue but lapse of twelve years.” b e c o m e s d a r k e r and darker until it is finally black if the ink contains enough iron and The present writer does not doubt the truth of these tannin. The change in color is due to the formation of statements about this particular set of checks but objects ferric gallotannate, whose black color hides the blue of the to categorical claims that the blue dye must perforce disappear within a given number of years. I n the examination dye more or less completely. The oxidation that causes the blackening does not cease of three letters, involved in a legal controversy, to find out when all the ferrous iron is converted into ferric, but pro- the kind of ink that had been used, it was found and reported ceeds a t a rate that depends upon the conditions under which that the writing still contained enough blue dye to produce the writing is kept. I n the dark the writing will last a great a stain on moist filter paper. The age of the letters was an deal longer than if it is exposed to bright light. I n either important point a t issue, and two handwriting experts immecase it is only a matter of time until the organic portion of diately deposed that the letters could not be 15 years old the writing is destroyed by oxidation so that only rusty because the dye had not all disappeared. marks are left, but, before this end is reached, the writing I n the meantime twenty-two samples of writing on dated goes through a series of color changes. It is not necessary pages of the writer’s laboratory notebooks a t the Bureau t o describe these changes, for the point of present interest of Standards had been examined ( I ) . The tests were made is the disappearance of the blue dye, which is destroyed before in the summer of 1932, on writing from April, 1905, to July, the black iron gallotannate becomes seriously affected. 1910, all well above 15 years old. I n each of the years except According to Mitchell and Hepworth ( 2 ) , “the black iron 1906 and 1909 one or more bits of writing gave a total of tannate is much more stable to atmospheric influences than nine positive tests for blue dye. Since then many more the dyestuffs used as provisional pigments, whereas the latter samples of known age have been examined, and are here usually offer greater resistance to chemical agents.” The reported. Blue dye may last a great deal longer than 15 chemical agent they seem to have had in mind is a 5 per cent years, and the absence of dye in a given sample of writing solution of oxalic acid. On the same page they describe does not necessarily prove that it is older than another the results obtained by treating a number of bank checks of sample in which there is a comparative abundance of dye. different ages with this solution. This reagent bleached the In other words, the presence or absence of dye in detectable ferric compound, while the dye dissolved in the acid solution. amount is not a safe criterion of the age of writing. BlueThey found that there “was very little diffusion [of dye] in black writing ink is not a substance of definite and fixed
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