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Metallographic Grinding and Polishing Guide

Learn the fundamentals of metallographic grinding and polishing, including mechanical preparation methods, grinding abrasives, polishing processes, consumable selection, surface preparation, and common polishing challenges.

Written by: Dr. Mike Keeble
Last Updated: August 2026
10 Comments
Reviewed by: Buehler Lab Team

Types of Metallography Preparation

Mechanical Preparation & Etching

Mechanical preparation is the most widely used method in metallographic sample preparation. This approach involves the systematic refinement of the sample surface through material removal, with the primary objective of eliminating deformation and damage introduced during prior processing steps. Material removal is achieved using abrasive media applied in progressively finer stages.. The sample may be examined in the polished state, or etching may be used to reveal microstructures. Chemical etching is most common, with a wide range of etchant recipes developed for each material to reveal specific structural detail.

Commonly used equipment and consumables in mechanical preparation include grinding and polishing systems, vibratory polishers, diamond grinding discs, silicon carbide (SiC) abrasive papers, and polishing cloths of varying types. Abrasives, such as diamond suspensions and final polishing oxide solutions, are also routinely used to achieve the desired surface quality.

The final surface condition is determined by the specific analytical requirements. For high-resolution microstructural characterization, specimens are typically prepared to a mirror-like, deformation-free finish that enables detailed observation. Alternatively, preparation may be terminated once the surface quality meets the requirements of a given inspection or testing method.

Cleaning and Drying

Cleanliness throughout the entire process is critical to avoid contamination problems. This includes the specimen, the user’s hands, and the equipment. After the last polishing step, the samples should be cleaned to remove abrasives and debris. This is typically achieved by swabbing with a liquid detergent solution following by rinsing under warm water, then with ethanol and dried in a stream of warm air. Alcohol can be used for washing if the specimen cannot tolerate water. Ultrasonic cleaning may be needed if the specimens are porous or cracked.

By optimizing the degree of preparation, metallographers can achieve accurate and reproducible results while balancing preparation time and resource efficiency. Appropriate selection of preparation parameters—including equipment, consumables, and process steps—requires careful consideration of both the material characteristics and the intended analysis.

Electrolytic Preparation and Etching (Traditional and NeoTerra)

Electrolytic preparation is less widely used than mechanical methods but offers distinct advantages for specific applications. Electrolytic polishing processes can provide rapid, effective, and highly reproducible surface preparation when properly controlled. These methods typically involve fewer processing steps.

Metallography Grinding and Polishing Machines

Manual Grinding and Polishing Machines

Manual grinding is the process of holding the sample to the preparation surface by hand. It was historically in widespread use, but it now typically only found in high-throughput laboratories as a means of eliminating the mounting step. Manual grinding requires a high level of operator skill to achieve consistent, high-quality results. In addition, manual grinding and polishing may introduce ergonomic strain and potential safety concerns. Manual techniques are based on long-established practices. The following guidelines provide key considerations for achieving successful results in manual grinding and polishing.

Semi-Automatic Mechanical Grinding and Polishing Machines

Semi-automated polishing systems enable high-throughput specimen preparation, providing improved consistency, superior surface quality, and reduced consumable usage compared to manual methods. These systems enhance surface flatness and edge retention, which are critical for accurate metallographic analysis.

Vibratory Polishing Machines

Vibratory polishing is an advanced metallographic finishing technique that produces a deformation-free surface with minimal operator effort. It is widely used for applications requiring high-quality surface finishes, particularly where preservation of microstructural integrity is critical. It can be used on any material or combination of materials but is particularly effective for preparing sensitive, soft, or ductile materials that are prone to deformation during conventional mechanical polishing.

Mechanical Preparation Methods

How to Grind and Polish Metallography Samples

It is important to choose the correct method for your material and for analysis. The chart below indicates recommended grinding and polishing steps by material type. See our SumMet guide for details on rotation direction, time and speed.
For details on these recommended methods see our SumMet guide.

Typical Grinding and Polishing Methods by Material

Group	Material	Grinding Steps	Polishing Step 1	Polishing Step 2	Polishing Step 3	Polishing Step 4
Electronic Materials	Non Populated Printed Circuit Board	CarbiMet 320 grit [P400] 600 grit [P1200]	TriDent™ 9µm MetaDi™ Supreme Diamond	TriDent 3µm MetaDi Supreme Diamond	ChemoMet™ MasterPrep™ Alumina
	Silicon in Micro-Electronics	CarbiMet 600 grit [P1200]	VerduTex™ 6µm MetaDi Supreme Diamond	VerduTex 3µm MetaDi Supreme Diamond	VerduTex 1µm MetaDi Supreme Diamond	ChemoMet MasterMet™ Silica
	Micro-Electronic Material	CarbiMet 320 grit [P400]	TexMet™ P 9µm MetaDi Supreme Diamond	VerduTex 3µm MetaDi Supreme Diamond	VerduTex 1µm MetaDi Supreme Diamond	ChemoMet MasterPrep Alumina
Ferrous & Non-Ferrous Materials	Soft Aluminum Alloys	CarbiMet 320 grit [P400]	TexMet C 9µm MetaDi Supreme Diamond	TexMet C 3µm MetaDi Supreme Diamond	TexMet C 1µm MetaDi Supreme Diamond	ChemoMet MasterMet Silica
	Nickel Based Superalloys	CarbiMet 240 grit [P280]	Apex Hercules H or S 9µm MetaDi Supreme Diamond	TriDent 3µm MetaDi Supreme Diamond	ChemoMet MasterMet Silica	—
	Titanium Alloys	CarbiMet 320 grit [P400]	UltraPad™ 9µm MetaDi Supreme Diamond	ChemoMet MasterMet Silica	—	—
	Copper & Copper Alloys	CarbiMet 220 grit [P240] - 320 grit [P400]	TexMet C 9µm MetaDi Supreme Diamond	VerduTex 3µm MetaDi Supreme Diamond	VerduTex 1µm MetaDi Supreme Diamond	ChemoMet MasterMet Silica
	Hard Steels	Apex DGD Red 75µm Diamond	Apex Hercules H 9µm MetaDi Supreme Diamond	TriDent 3µm MetaDi Supreme Diamond	MicroCloth™ MasterPrep Alumina	—
	Soft Steels	CarbiMet 320 grit [P400]	UltraPad 9µm MetaDi Supreme Diamond	VerduTex 3µm MetaDi Supreme Diamond	MicroCloth MasterPrep Alumina	—
	Cast Iron	CarbiMet 320 grit [P400]	TexMet C 9µm MetaDi Supreme Diamond	TriDent 3µm MetaDi Supreme Diamond	MicroCloth MasterPrep Alumina	—
	Heat Treated Steel	Apex DGD Red 75µm Diamond	Apex Hercules S 9µm MetaDi Supreme Diamond	MicroFloc 3µm MetaDi Supreme Diamond	—	—
	Stainless & Maraging Steel	CarbiMet 120 grit [P120] - 320 grit [P400]	UltraPad 9µm MetaDi Supreme Diamond	TriDent 3µm MetaDi Supreme Diamond	ChemoMet MasterPrep Alumina	—
Composites	Polymer-Matrix Composites	CarbiMet 320 grit [P400]	TexMet P 9µm MetaDi Supreme Diamond	VerduTex 3µm MetaDi Supreme Diamond	MicroCloth MasterPrep Alumina	—

Metallographic Grinding

The grinding abrasives commonly used in materials preparation are silicon carbide (SiC), aluminum oxide (Al₂O₃), composite ceramics and diamond. SiC is more readily available as waterproof paper than aluminum oxide although SiC particles, particularly with the finer size papers, embed easily when grinding soft metals, such as Pb, Sn, Cd and Bi. The abrasives may be bonded to paper, polymeric or cloth backing materials in the form of discs and belts of various sizes. Limited use is made of standard grinding wheels with abrasives embedded in a bonding material. When the abrasive is held in the polishing surface, it is called fixed abrasive grinding. The abrasives may also be used by charging the grinding surfaces with the abrasive in a premixed slurry or suspension. This is more typical of intermediary grinding and polishing stages.

Metallographic Polishing

Overview of the Polishing Process

Polishing is a critical step in preparing specimens for analysis, as it removes damage from the grinding process and ensures a smooth, shiny surface. The process typically involves several stages using progressively finer abrasives. Coarse and Intermediate polishing is intended to sequentially reduce deformation, and not create a shiny surface – scratches are expected in these stages.

Coarse Polishing: This initial stage removes the bulk of deformation caused by grinding. It uses larger abrasives on a hard napless polishing cloth.
Intermediate Polishing: This stage further reduces surface deformation and reduces scratches, often on a medium napless cloth with finer abrasive.
Fine Polishing: The final stage perfects the surface finish by eliminating any remaining traces of deformation using fine suspended abrasives on softer, often napped, surfaces.

Factors that influence the surface finish

Several factors can affect the quality of the polish, including:

Abrasive Size and Type: The choice of abrasives can significantly impact the final surface quality.
Cloth Selection: Cloth selection is critical to removal rate, flatness and deformation and is just as important as abrasive selection to specimen quality.
Polish Time and Load: The duration and pressure applied during polishing can significantly influence flatness and removal rate.
Rotational Speed and Direction: These parameters can affect the polishing quality and efficiency.

For detailed polishing methods tailored to specific materials see Buehler’s method by material section of the website.

Choosing Diamond Suspension

Diamond is routinely used for the preparation of most materials due to its high removal rate and low deformation depth. They are available in a wide range of micron sizes and two main diamond types. The micron size needed is determined by the material and end analysis goals.

Final Polishing

Final Polishing with Colloidal Silica vs. Alumina Abrasives

Final polishing suspensions are designed to remove the final layer of surface deformation. The removal of this deformation is essential for successful etching of sensitive materials and also when evaluating any sample with high magnifications, under polarized light or differential interference contrast, or for advanced analysis such as EBSD. Different types of final polishing suspensions employ different mechanisms for material removal.

Solutions to Common Issues in Metallography Polishing

Large Scratches

Large scratches remaining in the finer polishing stages may be a symptom of cross-contamination. Rinsing the specimen, specimen holder, and platen between steps can help clean out the larger diamond, reducing cross-contamination, If a specimen is cracked or porous, rinse in an ul trasonic bath for the minimum time required to rinse it clean. Extended ultrasonic cleaning time can damage the specimen. During the last 30 seconds of final polishing, stop applying additional suspension, replacing it with water to flush the cloth surface and rinse the specimen.

Relief

Relief is demonstrated by harder phases or constituents being left raised above the surface of the softer matrix. Prevent relief by reducing polish time, using a shorter napped cloth, or applying diamond paste rather than suspension.

Diamond Embedding

Embedding occurs when harder particles become engrained in softer material or cracks and voids. Using a more fixed abrasive, such as MetaDi Diamond Paste, or ultrasonic cleaning between stages can reduce the likelihood of embedding.

Smearing

Smearing is a superficial but significant form of damage that makes microstructural details less distinct, often caused by soft materials or poor lubrication. Smearing can be improved by using short napped cloths, vibratory polishing, or etching and then repeating the final polish.

Comet Tails

Comet tails are a result of poorly bonded, very hard phase in softer matrix; pores in matrix results in unidirectional grooves emanating from particles or holes; or excessive lubrication. To avoid this, use hard, napless cloths and/or reduce applied pressure. For porous materials, impregnate the pores with epoxy or wax.

Grinding and Polishing FAQs

Which grit should I start with for metallography?

Grinding should start with the finest grit size that will establish a flat surface and remove the effects of sectioning within a few minutes. An abrasive grit size of 180-240 (P180-P280) is usually coarse enough to use on samples sectioned by an abrasive wheel on a metallography saw – finer for very soft materials. For very hard materials such as ceramics and sintered carbides, choose diamond grinding disks with grit sizes from 125 to 75µm.

The table below shows recommended starting grit sizes for grinding different materials.

Why does metallography require multiple grinding and polishing steps?

In metallography preparation, the cutting step and each grinding step produces damage itself. The depth of damage decreases with abrasive size but so does the metal removal rate. Large gaps in abrasive size would require excessive time to remove the damage from the prior step and is inefficient. 3-5 steps from initial grind to final polish are typically sufficient for most materials. Note that for a given abrasive size, the depth of damage introduced is greater for soft materials than for hard materials, but removal rate is controlled by the harder material. This means that samples with combined softer and harder components often require more preparation steps.

What factors influence the surface finish in metallographic polishing?

Many factors influence the surface finish, such as:

Abrasive size and type
Cloth characteristics (weave, flatness and resilience)
Polishing time
Specimen load
Relative rotational direction
Rotational speed

If help is needed to determine the correct polishing recipe, please contact our applications specialists. Buehler Solution Centers provide materials preparation and analysis training to our customers worldwide. Our mission is to deliver valuable application solutions by employing Buehler methodologies.

What are the steps in a metallographic polishing process?

Polishing consists of two or more main stages, using successively finer abrasives.

Coarse polishing follows grinding and removes the bulk of the deformation created in the grinding process.
Intermediate polishing stages may be required to further reduce surface deformation and leave smaller scratches.
Fine polishing perfects the surface finish by removing any trace of deformation.

How do I know when to move to the next preparation step?

A specimen is ready to move to the next step once all the scratches are uniform and evidence of the previous step is gone. Final polishing on soft cloths should be performed for the minimum amount of time required to achieve the desired results, as over-polishing can damage the specimen.

How long does a polishing pad last?

Often, a cloth may get contaminated from improper care or gouged before showing significant signs of wear. End of life for a cloth is typically indicated by unusually high polish time, a degradation in result or signs of visible damage such as fraying.

10 Responses

Zex says:

July 19, 2023 at 3:36 pm

For Colloidal Silica used in the final polishing, if flushing it with water during the last 10-15 seconds to remove the silica on the surface, will pitting occurs in that circumstances?

Reply
1. Dr Mike Keeble says:
  
  July 24, 2023 at 2:54 pm
  
  No, we would not expect pitting to occur with flushing. It’s possible that you are seeing a different problem. Please contact us at lab.us@buehler.com with further details and we can assist further!
  
  Reply
Vancouver Anodizing says:

August 16, 2023 at 12:00 am

Buehler’s extensive reference to grinding and polishing is an invaluable tool for novices and experts in the field of materials science alike. Vancouver Anodizing Their knowledge and commitment to assisting readers in achieving exceptional outcomes in sample preparation are evident in this piece.

Reply
1. Dr Mike Keeble says:
  
  December 4, 2024 at 9:47 am
  
  Thank you, Vancouver. We pride ourselves on our expertise and sharing knowledge with the wider community
  
  Reply
Carolyn C. Cottrell says:

January 24, 2024 at 12:08 am

Thanks for sharing this insightful information

Reply
1. Dr Mike Keeble says:
  
  December 4, 2024 at 9:48 am
  
  Thank you for your comment!
  
  Reply
Ultra Touch says:

June 6, 2024 at 2:46 am

Fantastic guide! Clear, concise, and incredibly helpful. I’ve been struggling with grinding and polishing techniques, but this blog has provided me with valuable insights and tips. Can’t wait to apply them to my projects. Thanks for sharing!

Reply
1. Dr Mike Keeble says:
  
  December 4, 2024 at 9:49 am
  
  Thank you Ultra. You can find more extensive information in our Solutions section!
  
  Reply
Felice Contursi says:

December 2, 2024 at 3:49 pm

Hello, I’m texting from Penn State University. We have rectangular polyurethane samples and a polishing stone for manual polishing. We need a protocol to successfully polish the PU samples surfaces. Can you help us? We need to know which kind of abrasive sand paper we need, how and how long we should rub the samples on the paper and if we need to use only water or any other chemical (without altering the superficial properties of the material).

Reply
1. Dr Mike Keeble says:
  
  December 4, 2024 at 9:56 am
  
  Hi Felice – we have short guide for the preparation of polymers here:
  https://buehler.com/assets/solutions/Methods-by-material/19_SumMet_Polymers.pdf
  The steps given in Table 48 can also be applied using hand preparation.
  The approach outlined should work well for your samples. If you need additional support once you get started, please contact us directly!
  
  Reply