Contents
Fully compliant

DIN EN ISO 19403-2 paints and varnishes, part 2: determination of the surface free energy of solid surfaces by measuring the contact angle

Find the surface free energy of a paint, coating or substrate from contact angles, the measurement ISO 19403-2 describes. The Dropometer reads each angle with ±0.35° accuracy (Dropometer product specification), on a drop shape method validated in two peer reviewed papers, and you run OWRK in our free calculator.

What brings you here?

Who this is for
Paint and coating formulators, paint shops, pretreatment suppliers and substrate makers who need surface free energy.
Compliance tier
Fully compliant: the Dropometer measures the contact angles and you run OWRK in the free Contact Angle to Surface Energy Calculator.
Measurement
Sessile drop contact angles of two or more liquids, 10° to 175° range, ±0.35° accuracy (Dropometer datasheet).
Setup
About 2 minutes. Battery powered, 1 kg, runs in the conditioned lab next to your panels.
Last updated
October 20, 2026
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Free one page checklist for ISO 19403-2: which liquids to prepare, how many drops to place, the settings to lock and what to record. Made for coatings QC benches.

Talk to an expert

Book a 15 minute demo on your coating

Tell us your substrate, paint system and current surface check. We will measure live, run OWRK in the free calculator and tell you plainly where the Dropometer fits and where it does not.

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View the official standard
Gurdeep-Saini-Photo
Written by
Gurdeep Singh Saini
Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.
COO at Droplet Lab
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Droplet-Lab logo
Technical Review by
Droplet Lab Team
Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.
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Verified against ISO 19403-2: Paints and Varnishes
Gurdeep-Saini-Photo
Written By

Gurdeep Singh Saini

COO at Droplet Lab

Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.

Droplet-Lab logo
Reviewed By

Droplet Lab Team

Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.

Featured Studies & Publications

Research Paper Contact angle measurement with a smartphone
Research Paper Surface tension measurement with a smartphone using a pendant drop

Evidence box: ISO 19403-2 part 2 and the Dropometer

Standard

ISO 19403-2:2024, Paints and varnishes: Wettability: Part 2: Determination of the surface free energy of solid surfaces by measuring the contact angle, from ISO/TC 35/SC 9. Second edition, published September 2024, replacing ISO 19403-2:2017. Also published as EN ISO 19403-2:2024, and in Germany as DIN EN ISO 19403-2.

Compliance tier

Fully compliant. The Dropometer measures the contact angles of each test liquid. OWRK and Wu are not built into the Dropometer software: you run OWRK in the free Contact Angle to Surface Energy Calculator.

Instrument performance

Contact angle range 10° to 175°, accuracy ±0.35°, display resolution 0.01°. Pendant drop surface tension up to 75 mN/m, accuracy ±0.03 mN/m, for checking test liquids. From the Dropometer product specification.

Peer reviewed method

The drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers. See our validation publications.

Customer evidence

We have no published customer case for ISO 19403-2 yet. For the paint defect workflow, see how to stop fisheyes, craters and crawling.

What it does not tell you

Surface free energy shows whether a surface can be wetted. It does not measure paint adhesion. The standard also notes that rough or chemically uneven surfaces affect the result, and it excludes powders.

Executive summary

What this standard measures, who uses it and how the Dropometer fits

ISO 19403-2 finds the surface free energy of a paint, coating or substrate from the contact angles of two or more test liquids. Coating formulators, paint shops and substrate suppliers use it for the characterization of substrates and cured coatings, to see whether a surface is ready to wet and bond. The Dropometer is fully compliant with this measurement: it reads each angle with ±0.35° accuracy, and you run OWRK in our free calculator.

The 2024 edition asks for at least three drops of at least two test liquids from its liquid table. At least one liquid must have a polar part above 0 mN/m. If you use only two, the standard recommends water and diiodomethane. For polymers and coatings it prefers the Owens, Wendt, Rabel and Kaelble (OWRK) method or the Wu method. For background, read the surface free energy glossary entry and our surface energy measurement guide.

Neither OWRK nor Wu is built into the Dropometer software. You measure the contact angles with the Dropometer contact angle and surface energy kit and run OWRK in the free Contact Angle to Surface Energy Calculator. The Dropometer software itself calculates Equation of State, Fowkes and van Oss Chaudhury Good. To keep results comparable between labs, follow our notes on reproducible surface energy calculation.

When a paint crawls, craters or shows fisheyes, the cause often sits at the surface: see how to stop fisheyes, craters and crawling. Our paint guide covers wetting across common paint systems.

Further reading: why contact angle matters for coatings and adhesives QC, a surface free energy experiment with multiple liquids, surface free energy reference values for common polymers and how the Dropometer compares with the KRUSS Mobile Surface Analyzer.

How to measure the contact angle for ISO 19403-2

The ISO 19403-2 measurement, step by step, in our own words

From conditioned panel to an OWRK result

These steps outline the procedure. They do not replace the standard. Buy the current edition and follow its liquid table, drop dosing, camera setup and evaluation rules.

±0.35°

Contact angle accuracy

From the Dropometer product specification. Display resolution is 0.01°.

2+ liquids

Minimum the standard sets

At least three drops of at least two test liquids, one with a polar part above 0 mN/m (ISO 19403-2:2024).

Free

OWRK calculator

Enter your Dropometer angles in the Contact Angle to Surface Energy Calculator. OWRK is not built into the software.

1

Condition the panels

Keep test panels at 23 ± 2 °C and 50 ± 5 % relative humidity for at least 16 h, then test straight away, as the standard sets. Use panels of at least 4 cm × 4 cm where you can.

2

Check your test liquids

Pick at least two liquids from the standard's table, at least one with a polar part above 0 mN/m. Water must read at least 71.5 mN/m. Check the surface tension of liquids by pendant drop on the Dropometer, as described in ISO 19403-3.

3

Set up the Dropometer

Place the base plate on a level bench, mount the phone and LED, and use a clean syringe and needle for each liquid. Check focus and set the camera view as the standard specifies. Lay the panel flat on the sessile stage.

4

Place the drops and read the angles

The standard recommends the recently advanced angle. Place a drop, add liquid through the needle so its edge advances over dry surface, then let it rest. Automatic edge and baseline detection reads the left and right angles, so two operators get the same reading from the same image.

5

Repeat for each liquid

Place at least three drops of each liquid on fresh areas of the panel. Reject drops with bubbles or a poor fit. Record the mean and spread for each liquid.

6

Calculate and record

Enter the mean angles and liquid values in the free Contact Angle to Surface Energy Calculator to get OWRK dispersive, polar and total surface free energy. Record liquids, model, panel lot and room conditions, then compare with your limit.

7

Watch the full measurement

This video shows a complete Dropometer contact angle measurement, from setup to result. It covers the steps above in one run.

Dropometer contact angle measurement, start to finish. Repeat it with each test liquid.

Validated measurement approach

Independent benchmarking and publication-based validation references.

Peer reviewed method

The Dropometer drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers, one in Review of Scientific Instruments and one in Colloids and Surfaces A. Published contact angle accuracy is ±0.35°.

Read the validation papers

Customer evidence

We have no published client paper or case study on ISO 19403-2 yet. You can test the OWRK step yourself: enter angles from your own Dropometer runs in the free calculator.

Open the free calculator

Set wettability limits from your own paints and varnishes

ISO 19403-2 · surface free energy · coatings QC

ISO 19403-2 is a test method. Its public summary gives no pass or fail surface free energy, so set limits from your own correlation study (source: ISO 19403-2:2024 listing).

Measure panels that passed your adhesion test and panels that failed, with the same liquids and the same model. Set the accept limit on total and polar surface free energy from that data. Our reference values for common polymers help as a sense check, not as a limit.

The standard includes repeatability and reproducibility limits and a worked OWRK example. Use them to judge whether a change between lots is real. Repeat your study when you change resin, primer, cleaner or pretreatment.

Example output

Example data for illustration only. These are not measured results. Your own coating, liquids and limits decide the numbers.

Example: primed steel panels, water and diiodomethane, OWRK

Panel Water angle (°) Diiodomethane angle (°) Polar (mN/m) Total SFE (mN/m) Decision
Reference, adhesion passed72.039.86.546.2Reference
Panel A, abraded and wiped58.033.612.455.1Accept
Panel B, as received78.044.24.742.1Clean and retest
Panel C, silicone contact96.063.61.427.9Hold, find the source

How to read this table

Each angle is the mean of three drops, the minimum the standard sets. Surface free energy is OWRK with the standard's liquid values for water (72.8 mN/m: 21.8 dispersive, 51.0 polar) and diiodomethane (50.8 mN/m, all dispersive). The decision uses an example limit of 44 mN/m total and 5 mN/m polar, set from an adhesion correlation.

Example output chart

The same example data as the table, split into dispersive and polar parts.

Grouped bar chart of example dispersive and polar surface free energy for four primed steel panels, showing the silicone contaminated panel with the lowest values

Example data, not measured results.

Business impact

What changes when surface readiness is a measured energy

Metric Before Dropometer With Dropometer Results
How readiness is checked Test inks or a water break test, read by eye Contact angles of two or more liquids, read from the drop image No published benchmark
Result format Pass or fail Dispersive, polar and total surface free energy in mN/m ISO 19403-2 OWRK method, run in the free calculator
Angle reading Shared lab goniometer, booked in advance ±0.35° accuracy, 0.01° display, on the bench next to your panels Dropometer product specification
Test liquid check Taken from the bottle label Pendant drop surface tension up to 75 mN/m, ±0.03 mN/m Dropometer product specification

See the measurement on your own panels

Bring a panel that painted well and one that did not. We will measure both live and run OWRK in the free calculator.

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ROI estimate

Estimate the cost of the paint adhesion failures this test can catch

Enter your own numbers. The defaults are examples, not Droplet Lab results.

Quality cost snapshot

Estimate what wetting related failures cost you.

Example only. Use what you see in a trial on your own samples.
Your own figure.
Your own estimate.

Result

~0
Estimated annual cost today
~0
Estimated annual cost avoided
~0
Payback period

Annual exposure combines audit/CAPA cost, customer rejections, and recall probability; avoided exposure applies the risk reduction percentage.

Method settings for contact angles on solid surfaces

Lock these before you compare results between lots or sites

Parameter Recommended Setting Technical Rationale
Test liquids At least two from the standard's table; water and diiodomethane if only two The liquids must differ in polar and dispersive parts, and at least one must have a polar part above 0 mN/m.
Liquid quality Analytical grade or better; water at least 71.5 mN/m The standard asks for measured values within ±2 % of the table. Check them by pendant drop.
Drops per liquid At least three, on fresh areas This is the minimum the standard sets. More drops narrow the spread.
Drop volume As the standard specifies, fixed for every drop The standard doses in the microlitre range. A changing volume adds spread that is not about the surface.
Angle type Recently advanced angle, or the static method as the standard specifies The standard recommends the recently advanced angle because it has the least operator influence.
Fit model Young-Laplace or polynomial, the same for every run Both models are in the Dropometer software. Do not mix them within one study.
Surface energy model OWRK in the free calculator The standard prefers OWRK or Wu for polymers and coatings. Neither is built into the Dropometer software.
Climate 23 ± 2 °C and 50 ± 5 % RH, panels conditioned at least 16 h The Dropometer runs at 10 to 45 °C and has no temperature or humidity control. Condition the room.

Is ISO 19403-2 the right test?

Pick the method by the question you need answered

Start: What do you need to know about the surface?

Polar and dispersive surface free energy

Signals:

You need to know why a paint wets or fails to bond, not just whether it wets.

Rule-out:

Use ISO 19403-2, this page. The Dropometer is fully compliant: it measures the angles and you run OWRK in the free calculator.

Advancing angle as a wettability check

Signals:

You want one liquid and one advancing angle to compare coatings, substrates or pigments.

Rule-out:

Use ASTM D7334.

Surface tension of the paint itself

Signals:

Craters or fisheyes point to the liquid paint, not the substrate.

Rule-out:

Measure the paint by pendant drop to ISO 19403-3.

Fast pass or fail before painting

Signals:

You need a quick check on plastic parts at the line and a mN/m level is enough.

Rule-out:

Test inks to ISO 8296 are a common quick check. Contact angle complements them.

Decision tree at a glance

Start from the question you need answered. Blue boxes are measurements the Dropometer runs.

Decision tree for choosing between ISO 19403-2 surface free energy, ASTM D7334 advancing contact angle, ISO 19403-3 pendant drop surface tension and ISO 8296 test inks

Is ISO 19403-2 the right test?

Interpreting the determination of the surface free energy

What the numbers tell you, and what they do not

The polar part tracks surface chemistry: Cleaning, abrasion and plasma usually raise the polar part. Release agents and silicones pull it down.
Total alone can mislead: Two surfaces with the same total can differ in polar part and wet a water borne paint differently.
Compare like with like: OWRK and Wu give different numbers from the same angles, and so do different liquid pairs. Record both.
Surface energy is not adhesion: A high surface free energy shows the surface can be wetted. It does not prove the paint will bond.
Expert perspective

Why surface energy decides whether paint bonds

Adhesion fails at the interface long before it fails in the joint; surface energy tells you whether that interface was ever ready to bond in the first place.

Dr. Alidad Amirfazli

Department of Mechanical Engineering, York University, Co-founder and Scientific Advisor, Droplet Lab

Limits of the DIN EN ISO method and of the Dropometer

Honest limits of the method and of the Dropometer

Rough, porous or uneven coatings give apparent angles. The standard notes this, and it excludes powders.
The Dropometer has no temperature or humidity control. Condition the room to the standard climate and record it.
OWRK and Wu are not built into the Dropometer software. Run OWRK in the free calculator and record the liquid values you used.
The 2024 edition removed ethylene glycol from the test liquids. Check older procedures and liquid lists before you start.
The camera runs at 10 frames per second. That suits a drop at rest, not millisecond spreading or absorption studies.
FAQ

Frequently asked questions

What does ISO 19403-2 measure?

It finds the surface free energy of a solid surface, such as a substrate or a cured coating, from the contact angles of several test liquids. The result splits into dispersive and polar parts. Contact angles on powders are outside its scope.

How many test liquids does ISO 19403-2 require?

At least two, from the liquid table in the standard, with at least three drops of each. At least one liquid must have a polar part above 0 mN/m. If you use only two, the standard recommends water and diiodomethane.

Can the Dropometer run ISO 19403-2?

Yes, at the fully compliant tier. The Dropometer measures the contact angles with ±0.35° accuracy. OWRK and Wu are not built into the Dropometer software: you run OWRK in the free Contact Angle to Surface Energy Calculator. The software itself calculates Equation of State, Fowkes and van Oss Chaudhury Good.

Should I use OWRK or Wu for ISO 19403-2?

The standard prefers either for polymers and coatings. OWRK is the more common choice, and you can run it in our free calculator. Wu is not in the Dropometer software or the calculator, so if your customer names Wu, calculate it from the same angles in your own tools. Whichever you pick, keep it for the whole study.

What changed in ISO 19403-2:2024?

The second edition replaced the 2017 version. It adds a definition of the recently advanced contact angle, removes ethylene glycol as a test liquid, sets a preferred minimum specimen size of 4 cm × 4 cm and adds guidance on camera tilt (source: ISO listing and the edition foreword).

Does a high surface free energy guarantee paint adhesion?

No. It shows the surface can be wetted by the paint. Adhesion also depends on cure, film build and the interface itself. Keep your cross cut or pull off test, and use surface free energy to catch poor surfaces before you paint.

Legal note

This page summarises ISO 19403-2 in our own words and does not reproduce the standard. Buy the current edition from ISO or your national standards body before you write a procedure. Droplet Lab does not certify compliance. Your own method validation does.

View the official standard Book a 15 minute demo

How this page was created

Sources, review and tools

Transparency 4 checklist items
01

Sources

ISO 19403-2:2024 listing; EVS-EN ISO 19403-2:2024 listing; SIST EN ISO 19403-2:2025 sample (liquids, drops, conditioning, foreword changes); ASTM D8597-24 listing, the Dropometer product specification and Droplet Lab validation papers.

02

Drafting assistance

Drafted with Claude (Anthropic) from the sources listed, then reviewed by Droplet Lab.

03

What we did not do

We did not copy text from the standard. Buy the current edition for the full procedure.

04

Last checked

October 2026

Report a correction

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Correction Request

We work hard to keep this page accurate and up to date. If you spot an error (wrong revision/year, missing requirement, incorrect interpretation, or broken link), tell us and we'll review it.

Contact us to report a correction

References

1. ISO 19403-2:2024. iso.org/standard/87262.html
2. EVS-EN ISO 19403-2:2024 listing. evs.ee/en/evs-en-iso-19403-2-2024
3. SIST EN ISO 19403-2:2025 sample (liquids, drops, conditioning, foreword changes). standards.iteh.ai/catalog/standards/sist/07d2e028-2460-4475-9490-c4e1f
4. ASTM D8597-24 listing. store.astm.org/d8597-24.html
5. Droplet Lab. Peer reviewed validation papers in Review of Scientific Instruments and Colloids and Surfaces A. dropletlab.com/validation/publications/
6. Droplet Lab. Dropometer product specification, 2026. dropletlab.com/products/dropometer/