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Image of a rack of parts moving between vats during the anodization process

3M Extreme Masking Tapes for anodizing

Anodization baths are some of the toughest environments around and we make extreme masking tapes tough enough to stand up to them.


Why 3M Extreme Masking Tapes for anodization?

Because anodizing takes place in acid bath solutions, anything used to mask the surface must withstand the harsh chemical bath for as long as the part is immersed – and may also need to survive painting or other downstream processes. Whenever the mask is removed it should come off in one piece without leaving residue behind that requires extra removal steps. We invented masking tapes and our wealth of experience means we know how to create extreme masking tapes that meet these and other requirements.

  • Icon of a shield representing Reliability

    Tight manufacturing tolerances help our tapes to go on consistently and provide peace of mind that they’ll perform the same way, time after time.

  • Icon of an increasing bar graph representing Performance

    Whatever type of anodizing you’re doing, we have a tape made to provide excellent masking lines in those specific harsh conditions.

  • Icon of three arrows forming a circle and representing Productivity

    Our consistency helps prevent leakage and rework so you get more parts finished on time and on budget. Tapes also eliminate the curing time of liquid masking options.

Anodizing converts the surface of a metal to provide a durable, corrosion-resistant oxide finish; unlike paint that bonds to the surface but remains separate, anodization creates a distinct layer that’s part of the metal but also different from it. The finish is achieved by applying an electric current while dipping parts in an acid bath – so any section that shouldn’t be treated needs a tough masking tape for anodizing that can withstand this process.

  • Graphic image of an anode and two cathodes immersed in liquid and showing electrical charges for each
    • Hard, abrasion-resistant surface will not peel or chip
    • Electrically insulates the underlying metal
    • Avoids thickness of painting and plating processes
    • Color can be embedded for decorative purposes

    Aluminum and its alloys are the most common, but other nonferrous metals such as magnesium and titanium can also be anodized.

  • Click the red dots for more information
    A brief history of anodizing acids
    Click the red dots for more information
    Timeline marked at 1923, 1927, 1950s, 1970s and 1990 to show when major anodizing acid bath types were introduced

Chromic acid is the first commercial anodizing process to be patented


Sulfuric acid process is patented


Oxalic acid is introduced in Japan; used today as an additional acid for hardcoat anodizing


Phosphoric acid process is established; has hydration resistant oxides


Boric sulfuric acid process developed by Boeing for non-critical fatigue parts

Extreme Masking Tapes for all three common anodizing processes

Type I anodization involves a chromic acid bath while Type II and Type III anodization use sulfuric or other acids. Find more information about each type and appropriate 3M Extreme Masking Tape solutions using the tabs below.

Type I - Chromic

Type I or Chromic Acid Anodizing

  • Image of gloved hands removing 3M™ Anodizing Masking Tape 8985L, leaving sharp masked lines and no residue
    3M™ Anodization Masking Tape 8985L withstands chromic acid for excellent lines and one-piece removal

    Type I anodizing is the oldest anodization process; it involves a chromic acid bath and ramping up the applied voltage through specific steps throughout the process. It creates a very thin layer of 0.05 to 0.2 mils and provides excellent corrosion resistance. Type I anodization is common on precision machine components and metalworking components for the aerospace industry. The anodization layer can be dyed, though it is more difficult than with Type II; it can also be used as a pretreatment before painting.

    • Chromic acid at 95°F ramping from ~5V up to 40V at 5 to 7V/min
    • Very thin coating of 0.05 to 0.2 mils
    • Minimal impact on fatigue strength of components
    • Excellent corrosion resistance

    Typical uses include:

    • Metalworking components typically for aerospace industry
    • Precision machine components
    • Welded components/assemblies
    • As a paint or primer base

3M Solutions

Image of gloved hands dipping parts masked with 3M™ Anodizing Masking Tape 8985L; graphic reads ‘Mask 5x faster1’
Introducing 3M™ Anodization Masking Tape 8985L

An extreme masking solution for chromic acid anodization.


Liquid masking has met its match

Replace complex, messy liquid masking and the unpleasant odors that go with it: 3M™ Anodization Masking Tape 8985L is transparent for easy, accurate positioning and has no cure time so the overall masking and de-masking can be done up to five times faster1. The ease of application and clean, one-piece removal could save up to 60%1 on labor time and associated costs.

  • Animation of a die-cut piece of 3M™ Anodizing Masking Tape 8985L being applied and removed from a round metal part
    • Engineered for chromic acid anodization
    • Clear purple backing for easy placement and visibility
    • Non-silicone rubber adhesive
    • Sharp masking lines minimize leakage and rework
    • Clean one-piece removal
    • Works with or without chemical film on a variety of aluminum and other metal alloys
    • Non-silicone release liner for easy die-cutting

Graphic showing cost savings example using 3M™ Anodizing Masking Tape 8985L ($20.15/sq yd) vs. liquid masking ($53.15/sq yd)

What's in our Extreme Masking Tape?

What goes into 3M™ Anodization Masking Tape 8985L and how do these features help you?

Click the red dots for more information.

  • Rolls of 3M™ Anodizing Masking Tape 8985L; text Transparent Polyester Backing, Rubber Adhesive, Non-Silicone Release Liner
Transparent Polyester Backing
  • Tough carrier resists abrasion, tears, scratches, punctures
  • Operator can check performance (leakage) prior to demask
  • Visibility helps to get placement right the first time
  • Immediate identification with printed tape name and purple tint for visibility
Rubber Adhesive
  • Specially formulated to resist the harshest acid bath chemistries
  • Non-silicone adhesive won’t interfere with downstream painting or bonding processes
  • Good initial tack and holding strength
  • Clean removal when processing is complete
Non-Silicone Release Liner
  • No silicone to interfere with downstream processes
  • Provides stability for die-cutting
  • Easily create die cuts with onsite plotters

Type II - Regular

Type II or "Regular" Sulfuric Acid Anodizing

  • Image of gloved hands removing 3M™ Polyester Tape 8992, leaving sharp masked lines and no residue
    3M™ Polyester Tape 8992 stands up to Type II anodizing baths for sharp lines, then removes cleanly

    Type II anodizing is most commonly done using a sulfuric acid solution, though other acids and combinations of acids can be used. This “regular” anodization takes place at room temperature and uses 10-20 volts to create a layer 0.1 to 0.8 mils thick. Type II anodizing creates a harder finish than Type I and is used for military-grade components, shells for computers and other electronics, hydraulic valve bodies and mechanical hardware.

    • Sulfuric acid at room temperature, 10 to 20 Volts
    • Coating of 0.1 to 0.8 mil
    • Harder finish than chromic
    • Clear finish can be dyed
    • Inexpensive

    Typical uses include:

    • Hydraulic valve bodies
    • Military-grade components
    • Computer and electronic enclosures
    • Mechanical hardware

3M Solutions

Type III - Hardcoat

Type III or "Hardcoat" Sulfuric Acid Anodizing

  • Image of gloved hands applying 3M™ Vinyl Tape 471 prior to an anodizing treatment
    3M™ Vinyl Tape 471 is easy to apply for excellent masking results in Type III anodizing baths

    Type III anodizing is most commonly done using a sulfuric acid solution, though as with Type II other acids or combinations of acids can be used. This more-complicated process takes place in very cold conditions using up to 90 volts of electricity to produce a “hardcoat” finish up to 2 mils thick. The hard finish of Type III anodizing is extremely resistant to wear and corrosion and provides electrical and thermal insulation properties; it is typically used for internal engine parts, sliding parts, hinge mechanisms and blast shields.

    • Sulfuric acid at 0° to 32°F and up to 90V
    • Coating of up to 2 mils
    • Extreme corrosion resistance and durability
    • Can repair worn surfaces

    Typical uses include:

    • Engine internal parts (e.g. cams, pistons)
    • Sliding parts
    • Hinge mechanisms
    • Blast shields

3M Solutions

Meet the expert

  • Image of Meredith Opatz, Application Engineering Specialist for 3M Specialty Tapes

    Meredith Opatz

    • Application Engineering Specialist, 3M Specialty Tapes
    • How long have you worked on harsh environment processes and solutions for 3M? I’ve been at 3M for over 10 years – I started in our Regulatory department and I’ve been an application engineer for around 9 years. I started with powder coating and progressively transitioned into harsher environments such as anodization.
    • Why and how was 3M™ Anodization Masking Tape 8985L developed? We started working on this product over five years ago because we were noticing a trend of customer requests for masking solutions where existing tape products were not performing. Masking against chromic acid is challenging with requirements that a tape solution provide minimal leakage against chromic acid and clean one-piece removal, as well as the security of a non-silicone adhesive not interfering with downstream processes.
    • What excites me about this product is the customer excitement about the product. Customers have been engaged and a part of the product creation throughout its development. They have opened their anodization baths to our testing and provided feedback to every prototype created, so development would not have been possible without their support.
    • Why purple? Some people think we chose purple to support the Minnesota Vikings football team, but really it’s because I’m a huge Prince fan, so it’s a shout-out to a great Minnesota artist.
    • What do you love about your job? I never knew such a job existed. It is like going behind the scenes of “how’s it made” every day. I support several products that go into dozens of unique and different applications that people may or may not know about. It allows me to be creative and learn something new on a daily basis. I get to work one-on-one with customers to help them improve their processes and make their jobs easier. I’m proud of the products we create and how we influence lives.

Explore other Extreme Masking Tape applications

Powder Coating

Powder coating uses electrical attraction to apply free-flowing dry powder to a part which then passes through an oven so the powder melts to form an even paint surface. Not only must the masking tape prevent powder from reaching masked areas, but both the carrier and the adhesive must withstand the high oven heat (usually 400°F/204°C or higher for 5-30 minutes) without transferring to the part so the tape removes cleanly afterward.

Polyester Tape Family

Polyimide Tape Family

We're here to help.
Need help finding the right product for your project? Contact us if you need product, technical or application advice or want to collaborate with a 3M technical specialist, or give us a call at 1-800-831-0658.
Need help finding the right product for your project? Contact us if you need product, technical or application advice or want to collaborate with a 3M technical specialist, or give us a call at 1-800-831-0658.

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  • ¹ Up to 5x faster and up to 60% reduction in labor time both based on 3M internal data.