Cleanliness and Contamination

Silicone Contamination Detection and Residue Testing: Find Silicone Oil on a Surface Before Coating or Adhesion Fails

Silicone oil, lubricant and mold release films are invisible to the naked eye, yet they cause paint craters and adhesion failures. A water contact angle check flags a low energy film on the surface, so suspect parts are cleaned again or sent for laboratory analysis before paint, coating or bonding.

Who this is for: Quality control and process teams in automotive paint shops, electronics assembly and medical devices, and anyone coating or bonding plastic, polymer or metal parts.

Where it fits: After cleaning and before painting, coating, printing or adhesive bonding, and when tracing the source of a defect.

What it does not do: It does not identify silicone or measure how much is there. FTIR or XPS confirm the contaminant; contact angle shows where to look.

Method

Sessile drop water contact angle (WCA)

Standard

Supports the ASTM F22 water break test

Setup

About 2 minutes

Book a 15 minute demo Request a quote

Red painted panel hanging on a paint line, where silicone contamination can cause craters and fisheyes

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

How little silicone it takes to weaken a bond

0.1 mg/ft²

of silicone on the surface already affected the bond strength of two epoxies and a paint in booster motor tests by ATK and NASA.

Caldwell, Hudson and Cash, Adhesion Society annual meeting, 2003

97%

loss of epoxy to steel bond strength (24.6 to 0.81 MPa) after a silicone oil film of about 108 mg/m², in tests by ATK Aerospace Systems.

Anderson et al., ATK Aerospace Systems report M10-0557, 2012

83.1° to 24.1°

contact angle on titanium before and after plasma cleaning removed surface contaminants, measured with the Dropometer by Harvard researchers.

Ho et al., Biomimetics 10:571 (2025)

Sources: G. A. Caldwell, W. D. Hudson, S. F. Cash, Bond Sensitivity to Silicone Contamination, 26th Annual Meeting of the Adhesion Society, 2003 (NASA NTRS 20030064092); G. L. Anderson et al., The Effects of Silicone Contamination on Bond Performance of Various Bond Systems, ATK report M10-0557, 2012 (NASA NTRS 20120016452); K. Ho, T. Shiba, C.-Y. Chen, D. M. Kim, Biomimetics 10:571, 2025 (a customer publication that used the Dropometer). Figures come from these sources, not from Droplet Lab measurements.

Quick reference

What this silicone screen does and what it does not

A quick reference for quality, process and R&D teams checking fit before reading further.

Evidence Box

Problem this solves

Silicone oil, lubricant and release agent films that cause paint craters, dewetting and adhesion failures but cannot be seen.

Standard

ASTM F22 is a visual water break test for hydrophobic surface films. A water contact angle reading adds a number that supports the visual call.

Peer reviewed method

The Dropometer drop shape method was validated against a KRUSS DSA100E in two peer reviewed papers, in Review of Scientific Instruments and Colloids and Surfaces A.

Customer publication

Harvard researchers used the Dropometer to show contact angle falling as plasma cleaning removed contaminants from titanium (Ho et al., Biomimetics, 2025).

Customer case study

Harvard University's Center for Nanoscale Systems added a Dropometer to its shared facility; five labs used it in seven publications in under three years.

Honest limit

Contact angle flags a low energy film. It does not prove the film is silicone or measure its concentration.

Who this is for

What silicone contamination problem are you trying to solve?

Pick the card closest to your role. Each one points to the part of this page that answers it.

Quality manager

Craters and fisheyes show up after painting, and the line strips and redoes parts to recover surface quality. A contact angle check before the paint booth shows which parts or zones carry a film and helps uncover where the silicone comes from.

A clean reading does not rule out every cause of a paint defect.

Process engineer

Adhesive bonding or conformal coating fails on parts that looked clean. Screening the surface before dispensing shows whether a lubricant or release agent film is behind the adhesion failures.

Set gates from your own clean and contaminated parts, not a value from another line.

R&D or medical device engineer

Silicone lubricant is used on many medical devices and plastic parts, and it transfers easily. Contact angle shows whether cleaning removes it before you coat or bond.

Confirm a suspect film with laboratory analysis before you change a validated process.

Fit check

Is a contact angle screen right for your silicone problem?

It helps when you need a fast check of many parts for surface contamination by a low energy film. It helps less when you need to know exactly what the film is or how much is there.

Good fit if

Paint, coating or adhesive fails with craters, fisheyes or failure at the interface.

Silicone lubricants, mold release, sealants or hand creams are used near the line.

You need a fast screen on many parts, not a few laboratory samples.

You want to compare cleaning methods, wipes or solvent choices.

You need to map which zone of a part carries the film.

Less relevant if

You need to identify the contaminant or its concentration. Use FTIR or XPS.

The contaminant is hydrophilic and does not change how water wets the surface.

The substrate is already very water repellent, such as PTFE or silicone rubber.

Surfaces are too small, rough or curved to place a drop on.

Summary

How to detect silicone contamination before it causes a defect

The answer in under a minute.

Silicone has a very low surface energy, so even an invisible film makes a surface repel water and stops paint, coating or adhesive from wetting it. Measure water contact angle on the cleaned surface and compare it with a clean reference. A higher angle means a film is present: clean again, or hold the part for laboratory analysis.

Contact angle is a screen, not an identification technique. It tells you a film is there and where, so FTIR or XPS testing goes to the right parts. It adds a number to the visual ASTM F22 water break test, and the Dropometer contact angle kit runs it at the bench or beside the line. Our contact angle measurement guide explains the method. Harvard researchers used the Dropometer to track contaminant removal; read our analysis of that paper and the Harvard shared facility case study.

Expert Quote

Expert perspective on invisible films

“

Because only the top few ångström decide wetting, an invisible contaminant film, even a monolayer picked up from the air, is enough to change how a liquid behaves on the surface.

The problem

Why silicone contamination stays invisible until a defect appears

Silicone-based products are common in manufacturing processes: lubricants, mold release agents, sealants, greases, sprays, hand creams and cosmetic products. Silicone oil spreads easily and moves from gloves, tools, packaging and the air onto parts. A film a few molecules thick is invisible to the naked eye, but its surface energy is so low that paint, coating and adhesive no longer wet the surface. The result is craters and fisheyes in paint, coatings that pull back, and adhesion failures, often found only after the part is finished. That is why silicone-containing products are largely banned from Space Shuttle booster motor production, according to ATK and NASA. Laboratory analysis using FTIR (fourier transform infrared spectroscopy) or XPS (x-ray photoelectron spectroscopy) can identify silicone, but it tests a few samples using swab or solvent sampling. Most lines have no fast check in between.

Craters or fisheyes appear in paint or clear coat.

A coating pulls back from edges or leaves bare spots.

Adhesive fails at the interface and the substrate looks clean.

Defects come and go by shift, line or material lot.

Water beads on a part that should be clean.

Troubleshooting

Root causes of silicone contamination and how to detect them

Why:

Silicone lubricant on fixtures, conveyors and moving parts transfers to parts by contact and spreads across the surface.

How to detect:

Water contact angle above the clean baseline near contact points, often higher on parts from one fixture or line.

Corrective action:

Use silicone free lubricants where you can and keep lubricated equipment away from parts. Our guide to sample prep and contamination control covers clean handling.

Why:

Silicone-based release agents leave a residual film on molded plastic and polymer parts.

How to detect:

The angle is raised evenly across the part, and is often highest on parts molded just after a release spray.

Corrective action:

Switch to a silicone free release agent, or add a cleaning or surface treatment step. Our experiment on contact angle on treated and untreated surfaces shows the size of change to expect.

Why:

Many hand creams and cosmetic products contain silicone, and operators transfer it with every touch.

How to detect:

High readings only at handled spots, with a wide spread across the part.

Corrective action:

Use gloves, keep silicone hand creams out of the work environment, and make that a written preventive rule for the line to prevent transfer.

Why:

Silicone is hard to remove. In ATK tests a solvent wipe raised epoxy to steel strength only from 0.81 to 10.9 MPa, against 24.6 MPa on clean steel.

How to detect:

The angle stays high after cleaning, or the high area grows.

Corrective action:

Use fresh wipes, a suitable solvent and a set wiping pattern. Add grit blast or plasma where your process allows, then recheck.

Why:

Sprays, curing sealants and silicone parts nearby can deposit films through the air in production environments.

How to detect:

Readings drift by shift or by plant area on parts no one has handled. Our contact angle reference values for common surfaces give a sense check.

Corrective action:

Map readings by area, move silicone processes away from the line, and cover parts in storage.

Why:

Some plastic and polymer grades contain a silicone additive or slip agent that migrates to the surface over time.

How to detect:

The angle rises with storage time, even on clean parts no one has touched. The wettability glossary entry explains why a thin film changes the reading.

Corrective action:

Check the material grade with your supplier, measure at a fixed time after cleaning, and set a maximum time before paint or bonding.

Not sure where your silicone comes from?

Bring a clean part and a suspect part to a call, and we will compare them on screen.

Book a 15 minute demo

Quality records

What a silicone screening record contains

Each check produces a record you can file with the part or batch. These records can feed into your existing quality records under ISO 9001, IATF 16949 or your site's quality system.

Part identity

Part number, material lot, zone measured and the next process step.

Cleaning details

Cleaning method, solvent and wipes, operator and time.

Method settings

Probe liquid, drop volume, spots and the reading time after each drop lands.

Readings

Contact angle at each spot, the median and the spread.

Decision

Release, clean again or hold for laboratory analysis, with the operator and date.

Drop images

Automatic edge and baseline detection gives the same reading from the same image, so a reviewer can recheck any result.

Measurements

What to measure to detect silicone on a surface

Primary check

Water contact angle (WCA) on the cleaned surface

Why it matters: Silicone films lower surface energy, so the water contact angle rises.

How to interpret: Compare with a clean reference of the same material and finish. There is no universal pass value; set gates from your own clean and contaminated references and adhesion results.

When it is not enough: It does not identify silicone or give its concentration.

Mapping

Contact angle across zones of one part

Why it matters: Handled spots, fixture contact points and edges often carry more film.

How to interpret: A median inside the gate with one high zone still means part of the surface is contaminated.

When it is not enough: Very small or curved features may not hold a drop.

Cleaning check

Change in angle before and after cleaning

Why it matters: It shows whether cleaning removes the film or only spreads it.

How to interpret: The angle should return to the clean baseline. If it stays high, change the cleaning method.

When it is not enough: Solvent left on the part gives a false low reading; measure only dry parts.

Confirmation

FTIR or XPS on parts that fail

Why it matters: FTIR identifies silicone from its infrared spectrum; XPS measures silicon in the outer few nanometres.

How to interpret: Use the spectroscopic result to confirm the source, then keep contact angle as the routine screen.

When it is not enough: Laboratory analysis is slower and tests a few samples, not every part.

Validation

Validated measurement approach for silicone screening

How the Dropometer itself has been validated, and where customers have published with it.

Peer reviewed method

The Dropometer drop shape method is published in Review of Scientific Instruments and Colloids and Surfaces A. Contact angle was validated against a KRUSS DSA100E, with a published accuracy of 0.35°.

See the validation papers

Customer publication on contaminant removal

Harvard researchers used the Dropometer to measure titanium before and after plasma cleaning removed surface contaminants; contact angle fell from 83.1° to 24.1° on machined discs (Ho et al., Biomimetics, 2025). The contaminants were not only silicone, but the principle is the same.

Read our analysis of the paper

QC Protocol

Implementing a silicone detection protocol on your line

Six steps for one material, one silicone source and one next process step. Repeat steps 1 to 3 for each new combination.

1

Lock the method

Fix the probe liquid, drop volume, reading time, spots per zone and drying time after cleaning.

2

Baseline clean parts

Measure parts you know are clean and that pass your paint, coating or adhesion test.

3

Make contaminated references

Contaminate reference parts with your suspected source at low and high levels, then paint, coat or bond them to see where failures start. Confirm the film with FTIR if needed.

4

Screen before the next step

Measure each part, zone or batch after cleaning, so problems are found in advance of paint, coating or bonding.

5

Release, clean again or hold

Release parts inside the gates. Clean again outside them, and hold repeat failures for laboratory analysis.

6

Trend and trace sources

Use the data collection to trend readings by zone, line, shift and material lot. Patterns point to the silicone source.

We completed our gage R&R study on the unit and it performed very well.

Brandon Barbee

Corporate Quality Engineer, Zeus Industries, Polymer Manufacturing

Download the silicone contamination screening SOP

A two page SOP you can adapt for your parts and silicone sources, with the method lock, gate setting steps, a troubleshooting table and a record sheet.

Contact angle measurement with the Dropometer

Example output

Example silicone screening log: several zones on one part

Example data only. Your gates and values will differ and must come from your own references.

How to read this log

Example gate: within 5° of the clean baseline with spread up to 4°. Green rows are released, amber rows are cleaned again, red rows are held for laboratory analysis.

Sessile drop contact angle measurement: DI Water on Nylon, left contact angle 50.1°, right 54.9°

Example zone screening log

Zone	Area	Spots	Median (°)	Spread SD (°)	Versus baseline	Result
Reference	Clean panel, paint adhesion confirmed	5	45.2	1.4	Baseline	Reference
Zone A	Centre, not handled	5	47.0	1.8	+1.8	Release
Zone B	Edge, handled at loading	5	63.8	6.1	+18.6	Clean again
Zone C	Near lubricated fixture	5	92.4	3.2	+47.2	Hold for analysis

Example data, not customer data. Water contact angles on a cleaned steel panel before painting, read at a fixed time after deposition.

Signal order

The order to check signals when you suspect silicone

Check these in order. Each one rules out a cause before you look at the next.

1

Contact angle versus clean baseline

Shows whether a low energy film is on the surface.

2

Zone to zone spread

Shows whether the film is local, at handled spots or contact points.

3

Before and after cleaning

Shows whether cleaning removes the film or spreads it.

4

Line, shift and lot trend

Links the film to a source: a fixture, an operator, an area or a material lot.

5

Laboratory confirmation

FTIR or XPS confirms whether the film is silicone on parts that fail.

FAQ

Common questions about silicone contamination detection

Questions quality and process teams ask before adding a contact angle screen.

How do you detect silicone contamination on a surface?

Detecting silicone contamination, including the detection of silicone oil residue, usually takes two levels. A fast screen, such as a water contact angle reading or the ASTM F22 water break test, shows a low energy film on the surface. Laboratory analysis using FTIR or XPS then confirms the film is silicone. Most teams screen every part or batch and send only the failures to the lab.

Can contact angle tell silicone apart from other oils?

No. Silicone, mineral oils, mold release and many other films all raise the water contact angle. The reading tells you a film is present and where it is. To confirm silicone, use FTIR, which shows silicone spectral bands in the infrared spectrum, or XPS, which measures silicon at the surface.

What is the limit of detection for a contact angle screen?

There is no single detection limit, because the change depends on the material, the silicone and how the film spreads. Find it for your process: make references at known low levels and record the lowest level that gives a detectable change. ATK and NASA tests found silicone as low as 0.1 mg/ft² affected some epoxy and paint bonds, so check that your gates react before bond degradation starts.

Is the water break test enough?

The ASTM F22 water break test is a quick visual check of a whole area and a good first screen. The result depends on the operator's judgement and is pass or fail. A contact angle reading gives a number you can trend, compare across shifts and use to set gates, so small changes show up before they become defects.

Where does silicone contamination come from?

Common sources are lubricants, release agents, sealants, sprays, hand creams, cosmetic products, packaging and some plastic additives. Silicone also moves through the air and on gloves and tools. Trending readings by zone, line and shift is the quickest way to find the source. Our automotive guide covers paint shop contamination issues.

Does this work across industries?

Yes. The same check is used in automotive paint shops, in electronics assembly before conformal coating or bonding, on medical devices where silicone lubricant is common, and on plastic parts before printing. Gates differ by material and process, so set them for each application.

What should we look for in an instrument for this screen?

A screening detection system should give repeatable readings across operators, use a published method, keep drop images with each result and be quick enough to use beside the line. Our guide to the best contact angle goniometer for industrial QA compares options.

Business impact

What changes when you screen for silicone contamination

Typical changes in how teams work. Benchmarks are given only where a published source exists.

Before and with a silicone contamination screen

Metric	Before Dropometer	With Dropometer	Indicative Benchmark
Screening before paint or bonding	Visual check or none	Contact angle on each part, zone or batch	Silicone at 0.1 mg/ft² affected epoxy and paint bonds (Caldwell et al., 2003)
Cleaning effectiveness	Assumed	Measured before and after cleaning	A solvent wipe restored epoxy to steel strength only from 0.81 to 10.9 MPa, against 24.6 MPa clean (Anderson et al., 2012)
Finding the source	Laboratory analysis after a defect	Readings trended by zone, line and shift	No published benchmark; track on your own parts
Samples sent to the lab	Many, chosen at random	Only parts that fail the screen	No published benchmark; track on your own parts

See the screen on your own parts

Bring a clean part and one you suspect. We will show the difference on a call.

Book a 15 minute demo

Estimate the cost of silicone related rework

Enter your own numbers. The result is an estimate, not a Droplet Lab claim.

Instrument cost ($) Each Dropometer unit is $5,000; the default models 1 unit.

Rework events / month Rework events per month that your own records trace to silicone or other low energy films.

Avg rework cost per event ($) Your own average cost to strip, clean and redo one part or batch.

Failures preventable (%) Use your own failure analysis; start low if unsure.

Scrap cost per event ($) Scrap cost per event from this contamination only, from your own records.

Other monthly savings ($) Other monthly savings you can show from your own records. Set to 0 if unsure.

Result

~0

Monthly savings

~0

Payback period

~0

First year net benefit

Monthly savings = preventable rework cost + preventable scrap cost + other monthly savings.

Limits

What contact angle cannot tell you about silicone

Honest limits, so you know when to reach for another test.

It does not identify silicone or measure its concentration.

Other films, such as oils, release agents, fingerprints and hand cream, give similar readings.

Very water repellent substrates leave little room for the angle to rise.

Rough or textured finishes change the angle; keep a baseline per finish.

Wet or solvent damp surfaces give wrong readings; measure only dry parts.

Gates do not transfer between materials, silicone sources or processes.

The check flags a low energy film and shows where it is. Identifying silicone, measuring its concentration and finding the root cause of every defect still need laboratory analysis and your quality process.

Book a 15 minute demo Request a quote

How this page was created

Editorial and technical transparency notes for this page.

Transparency Details 4 checklist items

01

Drafting assistance

Drafted with Claude Opus 5.5 (Anthropic) using web search for sources, then edited by the Droplet Lab team.

02

Technical review

Reviewed and edited for technical accuracy by the Droplet Lab Team.

03

Verification steps

Standard identifiers, units, thresholds and key procedural claims are checked against cited sources before publication.

04

Updates

Reviewed every 12 months or when the underlying method changes.

Report a correction

Spotted an issue in this summary? Send a correction request and our team will review it.

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

Sources

References

1.

Caldwell, G. A., Hudson, W. D., Cash, S. F. Bond sensitivity to silicone contamination. 26th Annual Meeting of the Adhesion Society, 2003. NASA Technical Reports Server 20030064092. https://ntrs.nasa.gov/citations/20030064092

2.

Anderson, G. L., Stanley, S. D., Young, G. L., Brown, R. A., Evans, K. B., Wurth, L. A. The effects of silicone contamination on bond performance of various bond systems. ATK Aerospace Systems, report M10-0557, 2012. NASA Technical Reports Server 20120016452. https://ntrs.nasa.gov/citations/20120016452

3.

Ho, K., Shiba, T., Chen, C.-Y., Kim, D. M. Plasma treatment to remove titanium surface contaminants and improve implant biocompatibility: an in vitro study. Biomimetics 10:571, 2025. Customer publication that used the Dropometer; the link goes to our analysis of the paper. https://dropletlab.com/validation/citations/analysis/plasma-treatment-to-remove-titanium-surface-contaminants-and-improve-implant-biocompatibility-an-in-vitro-study/

4.

ASTM F22. Standard test method for hydrophobic surface films by the water break test. https://dropletlab.com/industry-standards/astm-f22/

5.

Chen, X. et al. Contact angle measurement with a smartphone. Review of Scientific Instruments 89(3):035117, 2018. https://pubs.aip.org/aip/rsi/article-abstract/89/3/035117/368179/Contact-angle-measurement-with-a-smartphone

6.

Surface tension measurement with a smartphone using a pendant drop. Colloids and Surfaces A: Physicochemical and Engineering Aspects.

https://www.sciencedirect.com/science/article/abs/pii/S0927775717307744

7.

Droplet Lab validation papers

8.

Customer publications that cite the Dropometer

9.

ASTM F22 explained

10.

Harvard University shared facility case study

Silicone Contamination Detection and Residue Testing: Find Silicone Oil on a Surface Before Coating or Adhesion Fails

Featured Studies & Publications

How little silicone it takes to weaken a bond

0.1 mg/ft²

97%

83.1° to 24.1°

What this silicone screen does and what it does not

Evidence Box

What silicone contamination problem are you trying to solve?

Quality manager

Process engineer

R&D or medical device engineer

Is a contact angle screen right for your silicone problem?

Good fit if

Less relevant if

How to detect silicone contamination before it causes a defect

Expert perspective on invisible films

Why silicone contamination stays invisible until a defect appears

Root causes of silicone contamination and how to detect them

Not sure where your silicone comes from?

What a silicone screening record contains

Part identity

Cleaning details

Method settings

Readings

Decision

Drop images

What to measure to detect silicone on a surface

Water contact angle (WCA) on the cleaned surface

Contact angle across zones of one part

Change in angle before and after cleaning

FTIR or XPS on parts that fail

Validated measurement approach for silicone screening

Implementing a silicone detection protocol on your line

Lock the method

Baseline clean parts

Make contaminated references

Screen before the next step

Release, clean again or hold

Trend and trace sources

Download the silicone contamination screening SOP

Example silicone screening log: several zones on one part

Example zone screening log

The order to check signals when you suspect silicone

Contact angle versus clean baseline

Zone to zone spread

Before and after cleaning

Line, shift and lot trend

Laboratory confirmation

Common questions about silicone contamination detection

What changes when you screen for silicone contamination

Before and with a silicone contamination screen

See the screen on your own parts

Estimate the cost of silicone related rework

Estimate avoided rework and scrap from silicone related defects.

What contact angle cannot tell you about silicone

Standards, evidence and related cleanliness workflows

ASTM F22

Harvard University shared facility

Ho et al. (2025): our analysis

Dropometer

Cleanliness and contamination

Plasma treatment verification

Hydrophilic coating validation

Automotive guide

How this page was created

Drafting assistance

Technical review

Verification steps

Updates

Report a correction

References