‘That’s what we’re trying to find out,’ I said.
Chan took the cap off the small metal evidence button and with tweezers removed a layer of snowy cotton, revealing the two tiny bright turnings. She pushed back her roller chair to a counter behind her and proceeded to place a double-sided adhesive square of black carbon tape on a tiny aluminum stub. On this she mounted the shaving that seemed to have the most surface area. It was maybe half the size of a normal eyelash. She turned on a stereo-optical microscope, positioned the sample on the stage, and adjusted the light wand to take a look at a lower magnification before she resorted to the SEM.
‘I’m seeing two different surfaces,’ she said as she adjusted the focus. ‘One real shiny, the other sort of dull gray.’
‘That’s different from the Warrenton sample,’ I said. ‘Both surfaces were shiny, right?’
‘Correct. My guess would be that one of the surfaces here was exposed to atmospheric oxidation. For whatever reason that might be.’
‘Do you mind?’ I asked.
She scooted out of the way and I peered through the lenses. At a magnification of four, the metal turning looked like a ribbon of crumpled foil, and I could just barely make out the fine striations left by whatever had been used to shave the metal. Mary took several Polaroid photographs and then rolled her chair back to the SEM console. She pushed a button to vent the chamber, or release the vacuum.
‘This will take a few minutes,’ she said to us. ‘You can wait or go and come back.’
‘I’m getting coffee,’ said Marino, who had never been a fan of sophisticated technology and most likely wanted to smoke.
Chan opened a valve to fill the chamber with nitrogen to keep contamination, such as moisture, out. Next she pushed a button on the console and placed our sample on an electron optics table.
‘Now we got to get it to ten to the minus six millimeters of mercury. That’s the vacuum level needed to turn on the beam. Usually takes two or three minutes. But I like to pump it down a little more than that to get a really good vacuum,’ she explained, reaching for her coffee. ‘I think the news accounts are very confusing,’ she then said. ‘A lot of innuendo.’
‘So what else is new?’ I commented wryly.
‘Tell me about it. Whenever I read accounts of my court testimony, I always wonder if someone else had been on the stand instead of me. My point is, first they drag Sparkes into it, and to be honest, I was about to think that maybe he had burned his own place and some girl. Probably for money, and to get rid of her because she knew something. Then, lo and behold, there are these two other fires in Pennsylvania, and two more people killed, and there’s the suggestion all of it’s related? And where’s Sparkes been during all this?’
She reached for her coffee.
‘Excuse me, Dr Scarpetta. I didn’t even ask. Can I get you some?’
‘No thank you,’ I said.
I watched the green light move across the gauge as the mercury level slowly climbed.
‘I also find it odd that this psycho woman escapes from the loony bin in New York — what’s her name? Carrie something? And the FBI profiler guy in charge of that investigation suddenly ends up dead. I think we’re ready to go,’ she said.
She turned on the electron beam and the video display. The magnification was set for five hundred, and she turned it down and we began to get a picture of the filament’s current on the screen. At first it looked like a wave, then it began to flatten. She hit more keys, backing off the magnification again, this time to twenty, and we began to get a picture of the signals coming off the sample.
‘I’ll change the spot size of the beam to get a little more energy.’
She adjusted buttons and dials as she worked.
‘Looks like our shaving of metal, almost like a curled ribbon,’ she announced.
The topography was simply an enlarged version of what we had seen under the optical microscope moments earlier, and since the picture wasn’t terribly bright, this suggested an element with a lower atomic number. She adjusted the scanning speed of the live picture and took away some of the noise, which looked like a snowstorm on the screen.