Etching

[ Specific Etchants ] Common Etchants [ Etchant Database CD ] Product Description [ Home ]

Etching is a process for revealing the structure of the material, common etching techniques include:

Chemical
Electrolytic
Thermal
Plasma
Molten salt
Magnetic

The two most common techniques are chemical and electrochemical etching. Chemical etching is typically a combination of either an acid or base with an oxidizing or reducing agent in a solute such as an alcohol. Electrochemical etching is a combination of chemical etching with an electrical voltage/current.

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Common Etchants

There are a number of more common etching solutions. Several of them are listed in the folowing table.

The following table lists the most commonly used etchants

Etchant	Composition	Conc.	Conditions	Comments
ASTM No. 30	Ammonia Hydrogen Peroxide (3%) DI Water	62.5 ml 125 ml 62.5 ml	Mix Ammonia and water before adding peroxide. Must be used fresh. Swab 5-45 seconds	For etching copper, copper alloys and copper-silver alloys.
Kalling's No. 2	CuCl2 Hydrochloric acid Ethanol	5 grams 100 ml 100 ml	Immersion or swabbing etch at 20 degrees Celcius	For etching duplex and 400 series stainless steels and Ni-Cu alloys and superalloys.
Carpenters Stainless Steel Etch	FeCl3 CuCl2 Hydrochloric acid Nitric acid Ethanol	8.5 grams 2.4 grams 122 ml 6 ml 122 ml	Immersion etching at 20 degrees Celcius	For etching duplex and 300 series stainless steels.
Kellers Etch	Distilled water Nitric acid Hydrochloric acid Hydrofluoric acid	190 ml 5 ml 3 ml 2 ml	10-30 second immersion. Use only fresh etchant	Excellent for aluminum and titanium alloys.
Klemm's Reagent	Sodium thiosulfate solution Potassium metabisulfite	250 ml Saturated 5 grams	Etch for a few seconds to minutes	For etching alpha-beta brass, bonze, tin, cast iron phosphides, ferrite, martensite, retained austenite, zinc and steel temper embrittlement.
Kroll’s Reagent	Distilled water Nitric acid Hydrofluoric acid	92 ml 6 ml 2 ml	Swab specimen up to 20 seconds	Excellent for titanium and alloys.
Nital	Ethanol Nitric acid	100 ml 1-10 ml	Immersion up to a few minutes.	Most common etchant for Fe, carbon and alloys steels and cast iron - Immerse sample up from seconds to minutes; Mn-Fe, MnNi, Mn-Cu, Mn-Co alloys.
Marble's Reagent	CuSO4 Hydrochloric acid Water	10 grams 50 ml 50 ml	Immerse or swab for 5-60 seconds.	For etching Ni, Ni-Cu and Ni-Fe alloys and superalloys. Add a few drops of H2SO4 to increase activity.
Murakami's	K3Fe(CN)6 KOH Water	10 grams 10 grams 100 ml	Pre-mix KOH and water before adding K3Fe(CN)6	Cr and alloys (use fresh and immerse); iron and steels reveals carbides; Mo and alloys uses fresh and immerse; Ni-Cu alloys for alpha phases use at 75 Celcius; W and alloys use fresh and immerse; WC-Co and complex sintered carbides.
Picral	Ethanol Picric acid	100 ml 2-4 grams	Seconds to minutes Do not let etchant crystallize or dry –explosive	Recommended for microstructures containing ferrite, carbide, pearlite, martensite and bainite. Also useful for magnetic alloys, cast iron, high alloy stainless steels and magnesium.
Vilella’s Reagent	Picric Acid Hydrochloric acid Ethanol	1 gram 5 ml 100 ml	Seconds to minutes	Good for ferrite-carbide structures (tempered martensite) in iron and steel

Guide to Acid Concentrations

Acid / Base	Specific gravity	Concentration
Nitric (HNO₃)	1.4	68-70%
Hydrofluoric (HF)	-	40%
Hydrochloric (HCl)	-	37-38%
Ammonium Hydroxide (NH₄OH)	-	35%

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Etchant Database CD

For more specific etchants, PACE Technologies offers an CD etchant database containing over 2200 etchants.


Metallographic etchant and training CD

Etchant database search result		Metallographic training basics

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ETCHING PRODUCT DESCRIPTIONS

ETCHING / SPECIMEN PREPARATION
Description	Quantity	Catalog Number
Etchant / Specimen preparation CD	each	CD-ETCH

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Technical Information - Metallographic Etching

Metallographic Etching

Metallography Support

Etching