Sodium Rhodizonate Test
Definition
Colour test for lead. The cloth is treated with sodium rhodizonate followed by buffer; lead deposits give a pink-to-red colour, confirmed with dilute HCl turning the spot blue-violet. Maps the lead halo around the bullet hole.
- Test classification
- Confirmatory color test for lead in gunshot residue (GSR)
- Primary color reaction
- Pink or red complex with lead; turns blue-violet with dilute HCl
- Primary forensic use
- Maps lead halos around bullet holes to establish firing range and pattern
Common questions
How does the sodium rhodizonate test identify lead?+
The test uses sodium rhodizonate to form a pink or red complex when it contacts lead deposits. The color is confirmed by acidifying with dilute hydrochloric acid, which turns the spot blue-violet. This color change distinguishes lead from other gunshot residue metals.
What makes this test different from other GSR color tests?+
The sodium rhodizonate test specifically differentiates lead from barium and strontium through the acidification step. Only lead produces the characteristic blue-violet color after adding dilute HCl, making it a confirmatory rather than preliminary test.
How is sodium rhodizonate used at a shooting scene?+
The cloth or surface around the bullet hole is treated with sodium rhodizonate followed by buffer. Lead deposits appear as pink-to-red spots, which turn blue-violet when acidified, mapping the lead halo to help determine firing range and bullet hole pattern.
Related terms
- Modified Griess Test
- A contact-transfer colour chemistry test for nitrite-containing propellant combustion residue. Sulphanilic acid undergoes diazotisation with nitrous acid (from NO2 on the target...
- ASTM E1588
- ASTM International standard practice for gunshot residue analysis by scanning electron microscopy with energy-dispersive spectrometry. Defines particle classification (characteristic, consistent-with, indicative), morphology...
- Bullet Wipe
- Greyish to brownish ring of lubricant, lead and copper rubbed off the bullet onto the margin of an entry hole in clothing....
- Contact Shot
- Muzzle pressed against skin or clothing at the moment of firing. Hallmarks are a stellate (star-shaped) wound from sub-dermal gas tracking, a...
- Dermal Nitrate (Paraffin) Test
- Historical test where molten paraffin was cast on the suspect's hand and the cast was sprayed with diphenylamine in sulphuric acid. Blue...
- GSR
- Gunshot residue. The mix of particles ejected from a firearm on discharge, composed of primer metals (Pb, Ba, Sb), propellant residues (nitrites,...
- Powder Tattooing
- Stippling pattern of unburned and partially burned propellant grains embedded in the skin around an entry wound. Cannot be wiped off. Pathognomonic...
- Primer
- The small explosive cup at the base of a cartridge that ignites the propellant. Conventional primers use lead styphnate, barium nitrate and...
- Range of Firing
- The distance from the muzzle of the firearm to the target at the moment of discharge. Estimated from wound geometry, soot pattern,...
- SEM-EDX
- Scanning electron microscopy with energy-dispersive X-ray spectroscopy. The electron beam excites characteristic X-rays from each element present in the target grain, giving...
- Sintox Primer
- Lead-free, heavy-metal-free primer chemistry developed by RUAG. Uses diazodinitrophenol (DDNP), tetrazenes and potassium nitrate. Modern Sintox GSR particles contain Zn, Ti and...
- Soot (Blackening)
- Submicrometre carbon-rich particles from incomplete propellant combustion, deposited on the garment or skin surface around the entry hole at contact and near-contact...
Explained in these topics
- Determination of Range of Firing in Firearm CasesColour test for lead. The cloth is treated with sodium rhodizonate followed by buffer; lead deposits give a pink-to-red colour, confirmed with dilute HCl turni...
- Gunshot Residue (GSR) Analysis: Detection MethodsConfirmatory colour test for lead. A pink complex forms with Pb on contact; acidification with dilute HCl turns it blue-violet, which differentiates Pb from Ba...