Contents
Partially Compliant with Industry Standard

ASTM C813 Contact Angle Test Method for Hydrophobic Contamination on Glass

QC-ready sessile-drop contact angle measurements to detect sub‑monolayer hydrophobic residues on precision glass

Who this is for
Process engineers and QA/QC teams in optics, semiconductor, photonics, and display manufacturing especially those managing cleaning lines, coat/bond steps, and controlled environments (cleanrooms, ovens, storage, and tool bays).
Positioning
Dropometer does not replace ASTM C813. It supports an ASTM C813–aligned approach for water contact angles on glass to screen for hydrophobic organic residues that may be invisible to visual inspection supporting both process control (cleaning effectiveness) and environmental contamination monitoring via witness surfaces.
Last updated
February 18, 2026
Request Dropometer Quote View ASTM C813 Official Standard
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Standard intent (what the test method measures)

ASTM C813 is a test method for hydrophobic contamination on smooth glass surfaces using water contact angle measurement. When properly conducted, it enables detection of fractions of monomolecular layers of hydrophobic organic contaminants. Rough or porous surfaces may significantly decrease sensitivity; use this method primarily on smooth glass surfaces.

Dropometer role in workflow

Providing standardized image capture and automated reporting to support high-throughput QC, plus replicate statistics and zone tagging for product quality decisions. It does not replace ASTM C813.

Primary outputs

  • Water contact angle, θ (reported as an equilibrium contact angle per your site SOP)

  • Replicate spread (IQR or SD) across ≥N spots to reveal localized contaminant hotspots (handling, tool contact, airborne organics)

  • Optional: a contact angle map across the part surface for hotspot detection and failure analysis triage

Calibration requirement

Acceptance thresholds are process- and site-specific. Thresholds must be set using your own baseline + challenge data and risk tolerance:

  • Build a “known-clean” baseline distribution (defined zones, defined sampling plan)

  • Add realistic challenge modes (controlled contamination) and repeat

  • Set PASS / MONITOR / FAIL gates and document rationale
    Re-run correlation after major changes (new chemistry, new tool materials, new cleanroom polymer parts, or process drift).

Protocol defaults (starting point)

  • Test liquid: reagent water (avoid surfactant-containing water; control purity, storage, and containers)

  • Geometry: sessile drop on a horizontal glass surface

  • Timing: keep drop volume, placement, and timing consistent within your lab’s validated test conditions (report timing per SOP)

  • Replicates: multiple measurements per zone; ≥10 per critical zone is a common QC starting point for high‑risk bond/coat interfaces (site-defined)

  • Reporting: median θ + IQR (or SD) with zone labels (center/edge; bond ring; cassette position), plus lot/tool/shift, operator, time since clean

Known limitations

  • Sensitivity drops on rough/etched/frosted/porous surfaces; validate suitability for your glass family

  • Water purity and container cleanliness can distort readings

  • Handling dominates: glove/finger residues can create extreme localized angles—mapping + replicates matter

  • Baseline/fit stability matters: reject spots with distorted footprint, unstable baseline, or failed QC flag

Controls & Data Quality

  • Periodic water on clean PTFE as an equipment/technique stability check

  • A known-clean glass coupon/part control per run (site-defined)

  • Reject and re-run any spot where droplet footprint is distorted, baseline is unstable, or the fit/QC flag fails

How this page was created

Editorial and technical transparency notes for this page.

Transparency Details 3 checklist items
01

Drafting assistance

An initial draft was created with AI assistance (ChatGPT 5.2 Pro).

02

Verification steps

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

03

Updates

Reviewed every 12 months or when the underlying standard changes.

Executive Summary

ASTM C813 • contact angle • hydrophobic contamination on glass

This page helps you answer one practical question: Is this glass sufficiently clean—i.e., free of hydrophobic films—to support reliable coating, bonding, and downstream specification requirements?

The ASTM C813–style contact angle test is nondestructive: it screens surface cleanliness by measuring the contact angle of reagent-water drops. It may be used for control and evaluation of processes used to remove hydrophobic films, and may also be used for the detection and control of hydrophobic contaminants deposited from processing environments. It is sensitive to sub‑monolayer hydrophobic organic residue, making it suitable for high-value processes where trace films can drive coating non‑wetout, delamination, or bond failures.

Dropometer fits as a QC front-end: evaluate cleaned parts/coupons before irreversible steps (coating/bonding) and trend witness surfaces under defined ambient conditions to detect drift before yield excursions.

The Context

The interpretation premise is straightforward: clean hydrophilic glass is expected to show low contact angle behavior (near-zero contact angles under controlled measurement), while hydrophobic organic contamination increases measured contact angles.

This makes the method useful in two manufacturing contexts:

  • Screening for cleanliness and hydrophobic residue risk in cleaning process control

  • Monitoring processing environments: a surface free of hydrophobic films is exposed to the environment for a defined period and then tested

In both cases, the goal is practical: detect hydrophobic contamination on glass surfaces early enough to protect end use performance (adhesion, uniformity, optical throughput, electrical reliability, or corrosion-resistant coatings where applicable).

How Dropometer Fits the Workflow

We recommend using ASTM C813 as your standards anchor, and adding Dropometer as a QC front-end for screening + trending.

1

Cleaning process control (pass/fail before coat/bond)

Use case: Evaluate whether your cleaning recipe (solvent, detergent, megasonic, UV‑ozone, plasma) achieves a stable contact angle distribution consistent with your “known-clean” baseline.

Workflow (recommended):

  • Sample parts/coupons per lot, tool, or shift (site sampling plan)

  • Measure θ at defined zones (center/edge; bond ring; alignment fiducials)

  • Compare results to site-defined PASS/MONITOR/FAIL gates derived from a correlation study (see Calibration section)

  • If a FAIL gate triggers, hold parts and investigate handling, cleaning drift, and environment sources

2

Environmental contamination monitoring (witness surfaces)

Use case: Detect airborne organics/outgassing (for example, silicone vapors or plasticizers) that can deposit as hydrophobic films between clean and coat/bond.

Workflow (recommended):

  • Place witness coupons near ovens, storage racks, coating tools, or high-risk airflow zones

  • Expose for a defined time window (for example, an 8 h or 24 h shift window; site-defined)

  • Measure contact angles on the witness surface; trend θ over time and compare zones to localize sources

3

Root-cause triage (when defects appear)

Use case: Use contact angle maps and replicate statistics to separate handling contamination from process drift and environmental deposition.

  • If θ rises on parts but not on freshly cleaned controls, suspect handling/contact contamination

  • If θ rises on witness surfaces, suspect airborne organics or outgassing upstream

  • Use targeted experiments to evaluate suspected sources and document corrective actions

Validated measurement approach

Independent benchmarking and publication-based validation references.

Benchmark Validation

Our Contact angle and pendant‑drop surface tension methods have been benchmarked against KRÜSS DSA100E reference measurements.

See peer‑reviewed validation

Publication Evidence

Our instruments are referenced in peer‑reviewed journals, theses, and conference publications

Browse the full citations list

Calibration first (so your thresholds are defensible)

ASTM C813 • contact angle measurement • glass cleanliness thresholds

ASTM standards define how to run the method; acceptance thresholds remain process-specific. A short correlation study makes your gates defensible:

Step 1 — Build a clean baseline distribution (one shift)

  • Run ≥20 “known-clean” parts/coupons through your best cleaning process

  • Measure contact angles across defined zones and compute baseline statistics (median, IQR, tails)

Step 2 — Add realistic challenge modes (controlled contamination)

Introduce controlled, relevant contamination modes and repeat the same plan, for example:

  • gloved handling touch at known locations

  • controlled silicone exposure near an oven/tool

  • tool-contact transfer (fixtures, cassette rails)


Step 3 — Set PASS/MONITOR/FAIL gates

  • Choose thresholds that minimize false passes for your critical end use (coat/bond) and document the rationale

  • Re-run correlation after major changes (new chemistry, new tool materials, new cleanroom polymer parts, or process drift)


Step 4 — Ongoing instrument control

  • Trend PTFE contact angles and a known-clean glass control to detect drift in technique, optics, or dispensing

Example Output

Cleanliness Decision Gates Based on Contact Angle Drift

Gate Interpretation (site-defined) What to do
PASSθ within clean baseline windowRelease to coat/bond
MONITORθ drift above baseline, but below critical failHold; re-clean or investigate tool/handling
FAILθ indicates hydrophobic organic film riskStop + triage (environment + process)

QC-ready quick protocol (SOP card)

Goal: Repeatable detection of hydrophobic contamination on smooth glass surfaces by means of contact angle measurements, aligned with the current official standard revision used by your lab.

Sample handling

  • Apply a “no-touch” rule; use clean tweezers/fixtures and defined gloves

  • Record time since clean and storage/transport conditions (sealed, open rack, oven-dried, etc.)

  • Define exclusion criteria for visibly damaged or roughened areas

Setup

  • Stabilize part/coupon on a horizontal stage; define zone plan (center/edge; bond ring; fiducials)

  • Control lighting, baseline detection, and operator technique via training and routine checks

  • Always include controls: PTFE check + known-clean glass coupon/part control (site-defined)

Measurement (baseline method)

  • Deposit a reagent-water droplet (sessile drop) on the glass surface

  • Stabilize and image the drop and baseline

  • Determine θ per your validated analysis method

  • Keep drop volume, placement approach, and timing consistent within your lab’s validated test conditions (follow the current official standard revision used by your lab for exact parameters)

  • Use mapping + replicates (not single points) when handling or tool contact contamination is suspected

  • Treat this as a screening tool for hydrophobic contamination; corroborate with other methods when the failure mode could be inorganic, particulate, or chemistry-specific

Decision tree (probabilistic) — triage + rule-out checks

Start: θ trends upward, replicate spread widens, or a FAIL gate triggers.

Handling/contact contamination suspected

Signals:

localized hotspots; strong zone dependence (edges/handling points); large IQR.

Rule-out:

repeat with controlled handling; compare to a no-touch control stored under the same conditions.

Cleaning process drift suspected

Signals:

uniform θ shift across zones on freshly cleaned parts; controls shift together.

Rule-out:

evaluate chemistry concentration, rinse quality, bath life, drying protocol, and verify test liquid stability.

Environmental / outgassing contamination suspected

Signals:

witness surfaces drift upward with exposure time; strongest near ovens/storage/airflow transitions.

Rule-out:

isolate materials in the airflow path; check silicone sources; evaluate recent polymer/sealant/lubricant changes; shorten exposure windows to localize sources.

Method Settings (SOP-Ready)

Parameter Recommended Setting Technical Rationale
Standard ASTM C813 Defines contact-angle-based detection of hydrophobic contamination on glass using water contact angle measurement.
Geometry Sessile drop A water drop is deposited on the surface and contact angle is measured using imaging.
Test liquid Reagent water consistent with ASTM D1193 guidance (per site SOP) Water purity matters; surfactants/impurities can mask surface wettability.
Surface suitability Smooth glass only Surface roughness and porosity can reduce sensitivity; validate suitability for your glass family.
Timing Per validated site SOP; keep timing consistent and report it Contact angle values can depend on stabilization and measurement timing; consistency enables trending.
Replicates Multiple measurements per zone (site-defined; often ≥10 on critical zones) Localized contamination requires spot sampling; replicates support robust statistics.
Control check Water on clean PTFE + known-clean glass per run Technique stability check plus run control for drift detection.
Optional mapping Zone-based map across the part Supports hotspot detection, handling/tool-contact diagnosis, and failure triage.

Interpretation

Water contact angle, θ (per site SOP): Primary screening metric. Compare to your “known-clean” baseline distribution and site-defined PASS/MONITOR/FAIL gates.
Replicate spread (IQR or SD) across ≥N spots: Reveals localized hotspots (handling, tool contact transfer, airborne organics). Large spread often indicates contamination is not uniform.
Zone dependence / mapping (optional): Supports practical triage: edges/handling points vs uniform shifts vs environment-driven gradients (tool bay, oven proximity, airflow transitions).
Optional nuance (only if validated in your lab): Some teams track an advancing angle or hysteresis for added sensitivity; keep those methods separate from your compliance report under this method unless your SOP explicitly defines them.

Business impact — Before/After Dropometer

Metric Before Dropometer With Dropometer
Release decisions Visual inspection or downstream failures reveal issues late Nondestructive screening before coat/bond reduces late-stage surprises
Drift detection Environmental/handling sources found after yield excursions Trending witness surfaces + controls detects drift early
Root cause Handling vs cleaning vs environment unclear Zone tagging + replicate statistics + mapping accelerates triage
Rework / scrap risk Parts re-cleaned or scrapped after irreversible steps Hold parts at MONITOR/FAIL gates before irreversible steps
Documentation Ad hoc notes and subjective arguments Audit-ready templates + traceable numeric records (lot/tool/shift/time since clean)

Instant ROI Snapshot

Calculate your savings in real time.

Result

≈0
hrs/month saved
≈$0
/month ROI

Where do these numbers come from? i You enter your current total time per test (dispense + record + analyze + save). The calculator assumes that our Dropometer reduces that workflow to ~1.1 minutes per test (dispense + capture + automated fit + export). Time saved per test = max(0, your time − 1.1 min). Monthly hours saved = (monthly tests × minutes saved per test) ÷ 60, and monthly savings = hours saved × labor rate.

Common Pitfalls & Limits

Surface roughness / porosity: Rough, etched, frosted, or porous glass reduces sensitivity; do not treat this method as a general cleanliness detector on roughened optics.
Water purity: Impurities in the test liquid can distort contact angles; control reagent water, storage, and containers.
Handling dominates: Fingerprints and glove residues can create extreme localized contact angles; use mapping plus replicates, not single points.
Fit and baseline stability: Reject and re-run any spot with a distorted footprint, unstable baseline, or failed QC flag.
Scope discipline: Treat this as a screening tool for hydrophobic contamination; corroborate with other material testing when the failure mode could be inorganic, particulate, or chemistry-specific.

Legal note (no certification claim)

This page summarizes how Dropometer can support workflows aligned with ASTM C813 for hydrophobic contamination on glass by contact angle measurement. It does not reproduce ASTM text and does not confer ASTM certification. Always purchase and follow the official standard revision used by your organization, and establish site-specific acceptance thresholds through baseline and challenge studies.

Request Dropometer Quote View ASTM C813 Official Standard

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References

1. ANSI Webstore - ASTM C813
2. BSI Knowledge - current listing for ASTM C813-20(2024)

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