This post has info from Dan O. on the luminol footprint image treatment (Photoshopping, no details) [post 5011]:
Originally Posted by Numbers View Post
BTW, do you or anyone know whether the Forensic Police photoshopped the luminol CL prints to a uniform contrast/intensity? Did the cops admit to this data enhancement (or manipulation), or is it a conclusion based on the appearance of the images?
The image itself tells me all I need to know:
Date and time of data generation 20:31, 18 December 2007
Lens focal length 38 mm
Software used Adobe Photoshop CS Windows
File change date and time 15:32, 19 December 2007
Quote:
While I had read that the cops over-applied the luminol, I had thought that the high contrast indicated some high concentration of catalyst, such as umber, adherent to the floor material (tiles?) - maybe embedded in pores. Your comments and those of LondonJohn are dashing my hypotheses.
TMB and Luminol react to the same substances at nearely the same concentration. The two step TMB process gives a different indications for oxidants and catalysts that preak down the peroxide. For TMB not to react where Luminol does indicates that the substance is attached to the substrate and cannot be picked up by the TMB swab.
Be it rust, iron, umbra or very old blood, these all break down to the same thing: iron ions which can bond to other materials and act as the catalyst that releases oxygen from the peroxide that then combines with the Luminol to make it glow.
Quote:
ETA: That is, whatever caused the luminol to light up may be present in low concentration. It may have varied in concentration among the prints. It was not blood since TMB was negative. If Lab Tech Stefanoni et al. had thought there was any possibility the prints were blood, they would have used confirmatory testing on them.
It's clear they were told that the prints had to be blood. That's why they ignored the negative TMB result and went straight on to DNA testing. If there was other confirmatory testing done it has been properly concealed.
Originally Posted by Numbers View Post
BTW, do you or anyone know whether the Forensic Police photoshopped the luminol CL prints to a uniform contrast/intensity? Did the cops admit to this data enhancement (or manipulation), or is it a conclusion based on the appearance of the images?
The image itself tells me all I need to know:
Date and time of data generation 20:31, 18 December 2007
Lens focal length 38 mm
Software used Adobe Photoshop CS Windows
File change date and time 15:32, 19 December 2007
Quote:
While I had read that the cops over-applied the luminol, I had thought that the high contrast indicated some high concentration of catalyst, such as umber, adherent to the floor material (tiles?) - maybe embedded in pores. Your comments and those of LondonJohn are dashing my hypotheses.
TMB and Luminol react to the same substances at nearely the same concentration. The two step TMB process gives a different indications for oxidants and catalysts that preak down the peroxide. For TMB not to react where Luminol does indicates that the substance is attached to the substrate and cannot be picked up by the TMB swab.
Be it rust, iron, umbra or very old blood, these all break down to the same thing: iron ions which can bond to other materials and act as the catalyst that releases oxygen from the peroxide that then combines with the Luminol to make it glow.
Quote:
ETA: That is, whatever caused the luminol to light up may be present in low concentration. It may have varied in concentration among the prints. It was not blood since TMB was negative. If Lab Tech Stefanoni et al. had thought there was any possibility the prints were blood, they would have used confirmatory testing on them.
It's clear they were told that the prints had to be blood. That's why they ignored the negative TMB result and went straight on to DNA testing. If there was other confirmatory testing done it has been properly concealed.
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