CromaTest

Colorimetric reagent analysis · harm reduction

Educational tool. Reagents indicate the possible presence of a substance, not the purity, the dose, or the presence of adulterants. A colour is never a definitive confirmation: use multiple reagents and compare. No test makes a substance safe.

1 Which reagents did you use?

2 What colour did you observe?

Select at least one reagent above to enter the colours.

3 Compatible substances

⚠ The colour in a photo depends on lighting, white balance and screen: use it as an aid, not as truth. Photograph on a white dish under neutral light, then always confirm by eye. The detected colour is a suggestion: you can correct it in the analyser.

1 Reagent in this photo

2 Upload the photo of the result

Tap the coloured spot in the photo to sample the colour. 1st tap = main colour; 2nd tap (optional) = second shade if present.

3 Reagent readings

4 What it could be

Reference table: expected reaction of each substance with each reagent. Reactions can vary with batch, quantity, lighting and adulterants.

How to use it

  1. Place a grain of the sample on a white ceramic dish (not plastic).
  2. Add 1–2 drops of reagent. Watch the colour over the first 30–60 seconds: it often evolves.
  3. Repeat with a second and third reagent on separate samples: cross-checking the results reduces false readings.
  4. Enter the observed colours here and read the ranking of compatible substances.

What each reagent detects

Distinzioni di sicurezza chiave

  • MDMA vs DXM: with Marquis, DXM turns grey/black (slow), not purple. If you expect MDMA and see grey, suspect DXM.
  • MDMA vs methylone/cathinotes: with Marquis, methylone gives yellow, not purple.
  • LSD vs 25x-NBOMe: only indoles (LSD, DMT, mushrooms) react with Ehrlich (purple). Sold as LSD but Ehrlich negative → suspect NBOMe (very potent, dangerous).
  • MDMA vs PMMA/PMA: PMMA can mimic MDMA with Marquis (purple/black, slower); PMA reacts weakly. Both are highly toxic. Colours are not enough: a quantitative test is needed.
  • Cocaine: general reagents react weakly; confirmation requires the cobalt thiocyanate (Scott) test.
  • GHB/GBL and fentanyl: not reliably detectable with these reagents; dedicated tests are needed (e.g. fentanyl test strips — see below).

Fentanyl test strips (FTS) — false positives from meth and MDMA

Fentanyl test strips are immunoassays designed for urine, repurposed for harm reduction: a little of the sample is dissolved in water and the strip is dipped in. They are complementary to colorimetric reagents (which do not detect fentanyl), not a replacement for them.

⚠ False positive: methamphetamine and MDMA at high concentration make the strip antibody react → a "fentanyl positive" result even without fentanyl (cross-reactivity). d-methamphetamine (the street form, high purity) reacts at lower concentrations. Reported false-positive incidence ≈ 0–10% depending on batch and brand.

Concentration is everything. The false positive appears at high concentration, roughly ≥ ~5–10 mg/mL (≈ 0.5–1% weight/volume). The answer is to dilute more for meth and MDMA:

  • Standard (most substances): 10 mg in 5 mL of water (1 teaspoon) = 2 mg/mL (0.2%).
  • MDMA and methamphetamine: dilute ~4×, 10 mg in 20 mL (4 teaspoons) = 0.5 mg/mL (0.05%).
⚠ Do not overdo the water: excessive dilution can give a false negative — the strip fails to detect fentanyl that is actually present. This is a serious risk above all for people who are not opioid tolerant (stimulant users). Aim for the right point: dilute enough to avoid the false positive, not so much that the fentanyl is missed.

Reading: one line = positive (fentanyl detected), two lines = negative. Thresholds vary by batch/brand: always follow the instructions of the strip you are using and up-to-date protocols (e.g. DanceSafe). Some specific batches require even greater dilution.

Limiti

Colorimetric tests are presumptive: they confirm the probable presence of the most reactive substance, but a "correct" reaction does not rule out the simultaneous presence of other dangerous active ingredients (e.g. fentanyl in a sample). For quantitative analysis, rely on drug checking services (GC-MS, HPLC) where available.

CromaTest · reference database for harm reduction.
Data based on public literature on reagents (e.g. DanceSafe, Reagent Tests UK, ProTestKit). Always verify with multiple reagents. Non-commercial tool, no data leaves the device.