# Another CSI inspired question **URL:** \ **Category:** Factual Questions\ **Created:** [May 24, 2006, 7:31pm UTC](https://boards.straightdope.com/t/another-csi-inspired-question/358069 "2006-05-24T19:31:21Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Drum\_God](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drum_god/32/44_2.png) [@Drum\_God](https://boards.straightdope.com/u/Drum_God)\ **Post date:** [May 24, 2006, 7:31pm UTC](https://boards.straightdope.com/t/another-csi-inspired-question/358069/1 "2006-05-24T19:31:21Z")
You know the scene – it’s in nearly every _CSI: Whatever_ episode. The CSI guys are poking around the crime scene and they shine their special ultraviolet (?) flashlights around. The find a glowing pool of blood that was previously invisible using normal light. “He thought he cleaned this up,” says one wise CSI guy, “but he can’t clean up THIS!” Similarly, they use the magic lights to show up semen stains on the bedsheets (or wherever). So, why isn’t blood cleaned up? One episode showed evidence that the suspect used bleach to clean up the spilled blood of his victim. How hard does one have to try to clean up blood. A few months ago, I cut my my finger badly and cleaned up the mess in the kitchen sink. I also used a towel. If I shined an ultraviolet light in the kitchen sink, would it glow from the blood? What about the blood from food being prepared in the kitchen? Do all our bedsheets glow due to sexual relations long gone by, even if I’ve changed the sheets since the last encounter? What is actually glowing when they do this? After the suspect cleans up the mess and restores the scene to an outwardly normal appearance, what is left that glows for the CSI guys? ---
**Author:** ![EnderWay](https://avatars.discourse-cdn.com/v4/letter/e/d26b3c/32.png) [@EnderWay](https://boards.straightdope.com/u/EnderWay)\ **Post date:** [May 24, 2006, 8:12pm UTC](https://boards.straightdope.com/t/another-csi-inspired-question/358069/2 "2006-05-24T20:12:25Z")
> [@Drum God](#): > > You know the scene – it’s in nearly every _CSI: Whatever_ episode. > > The CSI guys are poking around the crime scene and they shine their special ultraviolet (?) flashlights around. The find a glowing pool of blood that was previously invisible using normal light. “He thought he cleaned this up,” says one wise CSI guy, “but he can’t clean up THIS!” Similarly, they use the magic lights to show up semen stains on the bedsheets (or wherever). This is a nice link! [http://www.crimescope.com/march%2015/Applications.htm](http://www.crimescope.com/march%2015/Applications.htm) > [@](#): > > Since body fluids like semen, saliva, and vaginal fluids are naturally fluorescent, the use of a light source offers a unique method for locating them … > …the visible range, it has a unique color band (wavelength) under which the blood stain will darken to enhance its contrast by approximately 4 times. This page tells about the chemical tests! [http://www.bradford.ac.uk/acad/chemistry/localaccess/pwrdreqd/FEESM/FEESM%20session6-2002.html](http://www.bradford.ac.uk/acad/chemistry/localaccess/pwrdreqd/FEESM/FEESM%20session6-2002.html) > [@](#): > > If present, the stain (blood) will be subjected to a presumptive test – a test for a presumed substance on the basis of appearance or circumstances. Two presumptive reagents are currently used: > > Leuco malachite green (LMG) / peroxide > > Kastle Meyer (KM) – phenolphthalein / peroxide > > A suspect stain is rubbed with a piece of dry filter paper and a single drop of the LMG (or KM) reagent is added followed after a few seconds by a single drop of the peroxide solution. A positive result for blood is indicated by a deep turquoise colour (for LMG) or pale pink colour (for KM). > [@](#): > > So, why isn’t blood cleaned up? One episode showed evidence that the suspect used bleach to clean up the spilled blood of his victim. How hard does one have to try to clean up blood. A few months ago, I cut my my finger badly and cleaned up the mess in the kitchen sink. I also used a towel. If I shined an ultraviolet light in the kitchen sink, would it glow from the blood? What about the blood from food being prepared in the kitchen? Do all our bedsheets glow due to sexual relations long gone by, even if I’ve changed the sheets since the last encounter? > > What is actually glowing when they do this? After the suspect cleans up the mess and restores the scene to an outwardly normal appearance, what is left that glows for the CSI guys? IMHO … WAG I think it’s all just microscopic … that is most surfaces just absorb so of the body fluids and no amout of scrubbing/bleaching will get rid of it! From what I’ve seen (on TV) and beleive that sinks (porcilin? & stainless steel) don’t absorb stuff … so CSIs are left to go into the drain, where the gunk there absorbs stuff!!