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A New Technique for Analyzing The Optical Spectrum of Stamp Inks US. 1861 Case Study Edward (Ted) Liston PhD, FRPSL 11/18/15 WHAT IS A SPECTROMETER? A Spectrometer is an optical Instrument that measures the reflectance of a sample that his placed at a focal point in the instrument. In our case, we have use of spectrometers made by the Foster + Freeman Co., Model “Visual Spectral ‘Comparator 6000”. This name will be shortened to VSC in this paper. In our work, a stamp is placed inside the instrument and light is shined on it. The amount of reflected light is then measured at 600 different Wavelengths (colors) in the visible to near infrared range. Those reflectivity data are then plotted to show the amount of light reflected at each color. This plot is called the “Spectrum.* The VSC also produces a table of the reflectance at each color. This table is the data that are used to calculate the “Average” and the “Difference” spectra. WHAT IS A SPECTRUM? Figure 3 shows 3 typical spectra as given by the VSC “Te light green i for “Burt Sienna” ‘The light eis or "yellow ron ode” “The lights for "Red ion oxie™ “These plots show the measured reflectance at sx hundred colors, fom 40hm a the lve dt very deep red at the lf end. The numbers atthe bottom ofthe pot inthe “rainbow are the "wavelength ofthe reflected ight" which are the units that reused in this paper. “These plots demonstrate the major problem wit he nema petra. They are very early alike eventhough they ae fom very diferent olor pigment. Also thy show very Title “informatio,” they ae just amy ines “The soliton io make ‘Differential spectra. % of Maximum Reflection IAP Figure 4: Plot of the average Reflectivity of Red Lead 400 450 500 550 600 650 700 750 Wavelength - nm |P Fgre§ Mastr Program for exculatng the relecviyo he Average data ‘ata fom SmaheoiaP. 58 stamp ruber wavelength gto. vg. tolect, ‘1.28880 Biome Be 3138656 ai3078 a1asse2 asin Bre 3163 suri suns 3190556, 3202 3210558, mim man soso 2276007 precy 10880 mare mr ozs Bagi 34a baer 3491067 Reflecvty ma 3124 3124 3122 3119 3125, 3138 3138 3135, 3140 3180 3185 3160, 3168 3178 3186 3195 3209 3223 wat 5258 mae at Evy et Ba par ped 3 3489 35.18 son an an an an an 3075 2078 Bard aon 2078 2076 2075 Dorr 308 3082 3085 3001 sor 3108 3a as 3135 3123 328 313 212 B01 mia mn m2 286 se mos? 28 2082 2076 2088 293 2096 2108 2124 2134 2145 2159 Bed 2185 2198 nis 22 216 Boe ar 28 Es 2s 2435 242 8 2429 2458 za 22 2a 2a at at 236 26 2s 2268 2a 2308 2323 zat 2359 2 2396 2418 24 2495 255 297 2536 254 256 2658 2674 2628 2846 28 2 2585 rast 14s 1357 ner 287 sor 1424 at aa 38 480 1509 1831 1555 1579 1602 1625 1855 teas ate yeas weer 1028 1068 1958 1982 002 tone a7 33 1738 i183 W182 i182 184 4805 1818 1828 teas 1878 1898 1928 1949 1978 1990 2028 256 2086 2238 2a 2st er 228 235 ee an 275 2434 2405 2698 1p Figure 6 Mastr Program fr calculating tho DIFForent . 58 stamp pumbor wavelength ctierence 000 800 00 00 0.00 003 004 004 0.08 0.06 006 0.05 08 240 or O08 0.00 033 O18 on ou 02 022 025 028 030 028 ore 022 025 ‘itorence Sptavg, reflectivity 010 ont 013 018 O43 O16 3129 3129 3132 3130 3140 3145 a15t 3157 3183 3180 aot mo 210 219 ne 250 26 ir 290 20 345 372 3602 3428 Bea pry pr “4100 a1a7 3124 3128 3122 3119 3125, 3138 3138 3135, 3140 3150 3155 3188 3078 3186 3495, 200 pr mat 258 35 mae m0 B40 sant 3331 3818 3435 pyr pr 3518 ‘ope aifeence 3129-3129"000 3132.31.296003 3196.31326008 31403196008 31453140 =005 3t5t-314s=008 3487 -3181=008 3191-3180 =010 IAP Figure 7 DIFF Plot of Red Lead #61 0.60 pe 0.50 = z 0.40 = = 0.30 i 0.20 +=} = o.10 : SEEEEEee 0.00 \ -0.104 0 700750. 0.20 \ [ASSESS SSS5 -0.30 0.40 = -0.50 ~ ~ — Wavelength - nm IAP Figure 8 Diff of Red Lead on Average data IAP Figure 8B, Average and Diff of Pigeon 100.00 80.00 60.00 40.00 20.00 0.00 20.0 -40.00 60.00 Percent of Maximum Reflection Blood #41 Wavelength - nM