Etchants for metallographic structure contrast

In metallographic preparation, etchants create the necessary contrast to selectively reveal micro- and macrostructures. Depending on the material and the target feature size (e.g., phases or grain boundaries, precipitates, deformation structures), chemical or electrolytic methods are used. Our selection covers standard reagents (e.g., Nital, Kroll, NaOH, oxalic acid) as well as specialized agents (e.g., Klemm I/II, Barker, V2A pickling agent, PAG QT²) for defined material systems and application tasks.

Macro etching

Macro etching up to approx. 30× is used to visualize cast structures, forging/rolling textures, segregation, or weld contours (including deep etching/impressions).

Macro etchants

• Adler: Cast iron, high-alloy and corrosion-resistant steels, nickel alloys (weld seam/coarse grain).
• Heyn: Steels (phosphorus segregation); spot test to detect the bonding layer. Product page
• NaOH 10–15%: Aluminum alloys (macro etching).

• NaOH 10% NaOH 10%
• NaOH 15% NaOH 15%

• Nital 3/5/10%: Unalloyed and low-alloy steels (weld seam/heat-affected zone).

• Nital 5% (aq) Nital 5% (aq)
• Nital 5% (alk) Nital 5% (alk)
• Nital 10% (aq) Nital 10% (aq)

Micro etching

Micro etching from ~50× for structure development using wet-chemical or electrolytic methods (grain-boundary/grain-face etching, immersion/wipe etching).

Micro etchants

• Kalling II: Ni-Cu alloys, nickel-based superalloys. Product page
• Klemm I: Unalloyed and low-alloy steels, cast iron (color etching, polarized light). Product page
• Klemm II: Copper alloys, soft solder joints (color etching, polarized light). Product page
• Kroll (incl. mod. RPS150): Titanium alloys (e.g., Ti‑6Al‑4V); also Al‑Cu contexts. Product page

• Kroll mod. RPS150 Kroll mod. RPS150

• Brass etchant: Cu‑Zn, Cu‑Be, pure Cu; beta phase is colored. Product page
• NaOH 5%: Aluminum alloys (micro etching). Product page
• Nital 1/3/5%: Unalloyed and low-alloy steels, cast iron (ferrite, pearlite, sorbite, troostite, martensite).

• Nital 1% Nital 1%
• Nital 3% Nital 3%

• PAG QT²: Quenched-and-tempered unalloyed and low-alloy steels (austenite grain boundaries); additionally reveals fiber flow and segregation in steels. More info
• V2A pickling agent: High-alloy Cr/CrNi steels, matching filler metals, austenitic cast materials. Product page

Electrolytic etching

Anodic etching in an electrolyte; material removal or thin surface films depending on the system, contrast via orientation-/phase-dependent reactions.

Etchants for electrolytic etching

• Barker: Pure aluminum, Al alloys (especially 5xxx); evaluate under polarized light. Product page
• NaOH 5%: Steels (sigma-phase indication depending on procedure). Product page
• Oxalic acid: Cr and CrNi steels (sigma phase is dissolved out; carbides minimally attacked). Product page

Application areas and reagent overview

• Unalloyed/low-alloy steels: Nital (1–5% alcoholic; 5–10% aqueous), PAG QT² (austenite grain boundaries, fiber flow, segregation), Klemm I (color etching), Adler (macro), Heyn (P segregation/nitrided layers), NaOH (electrolytic, sigma indications).
• Stainless steels (austenitic/ferritic/duplex): V2A pickling agent, Kalling, possibly oxalic acid electrolytically.
• Aluminum/light metals: Barker (electrolytic), NaOH, possibly Nital variants depending on the target.
• Copper/alloys: Brass etchant, Klemm II (color etching).
• Titanium/alloys: Kroll (incl. mod. RPS150).
• Process solutions: PAG QT² for reproducible, defined contrast goals.

Reference images and practical examples

• Microstructure database (search by material number): www.schmitz-metallographie.de/en/structures-database/

Notes on selection and process control

• Define the goal (matrix/phases/grain size), preparation state, concentration/carrier (aqueous vs. alcoholic), contact time, temperature, agitation
• Reproducibility: fresh batches, constant parameters, clean containers
• Safety: PPE, fume hood, disposal. Please observe the information sheet.
• Background knowledge: Internal processes during etching

Country and language availability (relevant for delivery)

• Label and Safety Data Sheet (SDS/MSDS) must be available in the official language. Only the etchants listed per country are deliverable. Reagents not listed will not be supplied there.
• Germany (de) & Belgium (de/fr/nl): Adler, Barker, brass etchant, Heyn, Kalling 2, Klemm I/II (ready-made/potassium disulfite/stock solution), Kroll, Kroll mod. (RPS150), NaOH 5–15%, Nital 1–5% (alcoholic), Nital 5% (aqueous), Nital 10% (aqueous), oxalic acid 10%, PAG QT², V2A pickling agent.
• Netherlands (nl): Adler, Kalling 2, Kroll, NaOH 5–15%, PAG QT², “Salpeterzuur” 1–5% (alcoholic)/5% (aqueous) as Nital equivalents, V2A pickling agent.
• France (fr): Acide nitrique 1–5% (alco.), 5% (aq), Adler, Décapant V2A, Kroll, NaOH 5–15%, PAG QT².
• Italy (it): Acido nitrico 1–5% (alcoh.), 5% (aq), Adler, Kroll, Mordente V2A, NaOH 5–15%, PAG QT².
• Spain (es): Ácido nítrico 1–5% (alcoh.), 5% (aq), Adler, Kroll, NaOH 5–15%, PAG QT², Decapante V2A.

Regulations, shipping, and availability

• Language/documentation requirement: No delivery without SDS/label in the official language.
• B2C: Shipping to private customers excluded.
• Minimum order value: DE €50; EU €150; below that, no processing.
• Shipping costs LQ/dangerous goods: DE €20.00 (dangerous goods), €15.00 (LQ, single type); EU: €35.00; CH/LI: €45.00; price adjustments possible.

FAQ on etchants

1. How long do etchants keep?
   – Unopened original containers are often very stable when stored properly (practically for years up to decades). For operational practice we conservatively assume 2 years unopened; after that, theoretically, decanting into a new, suitable bottle would be sensible. After opening, check regularly (color/turbidity), note the date, store tightly closed.
2. Are there minimum order values?
   – Germany: €50; EU: €150 — below that, no processing. Tip: Combine requirements from our full range (~3,000 items) to reach thresholds efficiently.
3. Custom formulations?
   – Possible. Initial costs: external MSDS creation incl. GHS label €500 (one-time); MSDS update every 2 years €150; minimum purchase: 5 liters per month. We review formulation, feasibility, classification, and packaging; quotation thereafter.
4. Why not every etchant to every country?
   – Legal requirements: SDS/label in the official language; country-specific dangerous goods/transport rules and internal approvals must be observed.
5. Shipping costs (LQ/dangerous goods)
   – DE: dangerous goods €20.00; LQ €15.00 (single type; limited quantity; not all etchants via DHL) — EU: €35.00 — CH/LI: €45.00 — price adjustments possible.
6. Practical examples & matching etchants per material: Microstructure database; search by material number (e.g., 1.4301, 3.2315). Link: https://www.schmitz-metallographie.de/en/structures-database/

Accessories

• Etching dishes/tongs/PPE/alcohols/lab timer/sets: Accessories in the shop

Information sheet on handling etchants

• Please note our information sheet: Go to info page

Contact us for application-optimized etching solutions and consulting.