The decision tree behind the tool, the four field tests it runs through, the seven glass and film formats it can identify, and the chemistry-and-mechanics reasoning behind why each one requires a different cleaning protocol. The protocol I run on every consulting visit, ported to software.
What the Tint & Coating Identifier does, in five points:
Substrate identification is the diagnostic that should run before any cleaning chemistry comes out of the bottle. The Tint & Coating Identifier exists so the homeowner does not have to take a chemistry course to do it.
The most common cleaning damage I see in my consulting practice is not from aggressive chemistry or careless technique. It is from a homeowner — sometimes a working cleaner — using a method that would be entirely safe on the glass they thought they were cleaning, and which turned out to be inappropriate for the glass that was actually there. The window was tinted with surface film, not factory-colored. The window had a low-E coating on a face the homeowner thought was bare. The window was laminated and the edge sealant was vulnerable to a solvent the cleaner had no reason to suspect. None of these are exotic situations. All of them are present in normal residential housing stock. All of them are misdiagnosed routinely.
The Tint & Coating Identifier is the tool we built to address this. It walks the homeowner through the same four-step visual decision tree I use on every consulting visit, identifies the glass format with reasonable confidence, and produces a cleaning-safety profile specific to that format. This piece is the methodology behind the tool — what each step is testing for, what the answers actually mean, and the chemistry-and-mechanics reasoning that connects the identification to the cleaning protocol.
If you are a homeowner who has run the tool and wants the longer encyclopedia treatment of the substrates themselves, my glass types piece is the deep reference. This piece is for the user who wants to understand why the tool asked what it asked.
The first question the tool asks is when the home was built. This is not a matter of historical curiosity. The era a window was installed strongly predicts what kind of glass is in it.
Pre-1990 housing stock is dominated by single-pane annealed glass, sometimes with original aluminum or wood storm windows added retroactively. Tempered glass exists in this stock but only in the locations where building code specifically required it — bath enclosures, sliding doors, lower lights of patio doors. Coated glass is rare. Window films, if present, are aftermarket additions — usually added in the 1980s or 1990s during energy-conscious retrofitting.
1990–2010 housing stock is the transitional era. Most windows in homes built or renovated in this period are double-pane assemblies with annealed inner and outer panes. Low-E coatings became common toward the end of this era, but their placement and quality varied substantially by manufacturer. Tempered glass appears in code-required locations; mass-tinted glass appears occasionally in higher-end construction.
Post-2010 housing stock is overwhelmingly double-pane with low-E coatings on the interior face of one of the two panes. Low-iron glass for visual clarity is increasingly common in higher-end work. Triple-pane assemblies appear in cold-climate construction (Minnesota, Montana, North Dakota, the Maritimes) and in passive-house construction throughout the country.
The era answer alone does not identify the glass. It biases the probabilities. A user who tells the tool their home was built in 1925 and that the windows have not been replaced is unlikely to have low-E coatings; the tool can deprioritize that branch of the decision tree.
The second question asks the user to look at the glass against a neutral background — a white wall, a sheet of white paper, an overcast sky — and identify whether the glass appears clear, slightly tinted, distinctly tinted, or noticeably reflective.
The visual reading separates four meaningful classes:
Clear glass — no perceptible color shift against a white reference. The default. Most residential glass.
Slight green or blue cast — the natural color of standard soda-lime float glass produced from iron-bearing sand. Visible on the edge of any cut piece of glass and faintly visible in transmission on large panes. Not a tint per se; the natural color of ordinary glass.
Distinct tint (bronze, gray, green, blue) — the glass has been intentionally colored, either by mass-tinting during manufacture or by aftermarket film application. The visual reading alone cannot distinguish these two; that's what step 3 is for.
Reflective / mirror-like character — the glass shows a perceptible mirror character when viewed from the brighter side. This indicates either reflective film (most common in residential), a heavily-loaded low-E coating with high visible reflectance, or a true reflective glass (uncommon in residential).
The tool branches at this step. A user who reports clear glass goes one way; one who reports tint goes another; one who reports reflective character goes a third. The branches converge later when the cleaning-safety profile is generated, but the decision-tree path depends on which class the visual reading lands in.
The third step is the test that identifies whether the glass is single-pane or double-pane, and — if double-pane — gives a useful clue about whether the glass is laminated.
The test is simple. Stand on one side of the window in dim ambient light, with a single bright point light source on the same side as the user (a flashlight, a phone flashlight, a clear-glass desk lamp). Look at the reflection of the light source in the glass. Count the reflections.
One reflection — the glass is single-pane. The light bounces off the front surface of the glass and returns. There is no second pane to produce a second reflection.
Two distinct reflections, one slightly behind the other — the glass is a standard double-pane IGU. The first reflection is from the front surface of the outer pane; the second is from the front surface of the inner pane (or the rear of the outer pane, depending on the geometry). The two reflections appear to overlap with a small offset.
Three or four reflections — the glass is either triple-pane (uncommon in residential outside cold-climate construction) or laminated (the polymer interlayer produces an additional reflection). The tool asks a follow-up question to distinguish these.
Two reflections with one strongly tinted — the glass is double-pane with low-E coating, and the coating's spectral reflectance is producing a visibly different reflection than the bare glass surface. This is one of the most reliable visual indicators of low-E presence in residential glass without specialty equipment.
The double-image test is the part of the methodology that surprises homeowners who have never been told to look for it. Once you see it, you cannot unsee it. Every double-pane window in your house produces this characteristic doubled reflection. Every single-pane window does not. The test takes about ten seconds per pane and is reliable to roughly 95% confidence in normal residential conditions.
The fourth and final step is the edge inspection, which identifies laminated glass and distinguishes mass-tinted glass from surface-applied film.
Looking at the cut edge of a pane, three formats produce three visually distinct readings:
Single-pane glass with no coating or film shows a uniform-color edge — the slight green tint of soda-lime glass, with no internal layers visible. The edge is one continuous piece.
Mass-tinted glass shows a uniformly colored edge throughout the thickness. A bronze-tinted pane shows bronze through the full edge depth; a gray-tinted pane shows gray. The color is in the glass, not on a surface of it.
Surface-applied film shows a clear glass edge with a thin colored layer at one face — typically the interior face. The film is visible as a distinct layer adhered to the glass, often with a slightly textured edge where the film was cut to fit. Older or peeling films may show edge lifting that makes the film's separateness from the glass obvious.
Laminated glass shows two distinct layers of glass with a thin (typically 0.030-inch) interlayer between them. The interlayer often has a slightly different optical character than the glass — a faint yellow tint, a slight cloudiness, or a barely-visible offset.
For a user inspecting a window in their home, the edge of the pane is usually accessible at the top or bottom of the sash, and the inspection takes another ten seconds. If the edge is not accessible — covered by trim, embedded in stucco, behind a frame element — the tool has a fallback path that uses additional surface tests to make the identification, with somewhat lower confidence.
The tool produces one of seven verdicts at the end of the four-step decision tree:
Each verdict produces a cleaning-safety profile that lists the specific chemistries and tools that are safe and unsafe for that format. The profiles are not generic; they are based on the published manufacturer guidance for each format and on the failure modes I have personally seen in my consulting practice.
The Tint & Coating Identifier has limits, and they are worth being explicit about.
It cannot identify low-E coatings on the exposed face of a single-pane storm window or a single-pane primary glazing. These are uncommon but they exist, and they require the same protective protocol as exposed films — mild detergent only, no aggressive cleaning. The tool's decision tree assumes that low-E coatings, where present, are on cavity-facing surfaces. For the rare case where this assumption is wrong, the tool's verdict is conservative-by-default — it recommends against aggressive cleaning when in doubt, which protects the coating if the assumption is wrong.
It cannot distinguish tempered from annealed glass without the user inspecting the corner stamp, which the tool prompts for and which is the only reliable identification method. If the corner stamp is not visible, the tool defaults to assuming tempered in code-required locations (bathrooms, doors, low-mounted glass) and leaves the question open elsewhere. The cleaning-safety profile is conservative when the question is open.
It cannot identify nickel-sulfide-prone tempered batches, glass with specific manufacturer defects, or glass with damage histories the homeowner is not aware of. These edge cases are properly the domain of a working cleaner doing in-person consultation, not a remote diagnostic tool.
It cannot identify the kind of post-installation modifications that aren't visible from the homeowner's side of the glass — applied security films installed during commercial occupancy and forgotten, low-E films retrofitted to the interior face during energy-efficiency upgrades, bird-safe films, anti-graffiti coatings on commercial storefronts. Where any of these are suspected, the tool routes the user to seek confirmation from the building owner or the previous occupant.
The tool's job is to do the eighty-percent identification that a careful homeowner can perform with their own eyes and a bright light source. The remaining twenty percent is consultation territory.
The five-minute glass identification protocol I run on every consulting visit was developed over my eight years working at a glass coating manufacturer in the Pacific Northwest, watching the failure modes that come back in technical-service inquiries. The substrate-identification questions are the questions our service team asked first, every time, before any chemistry advice was given. The order of the questions is the order that produces the most reliable identification with the least specialty equipment. The visual archetypes are the ones that proved most distinguishable in field conditions over thousands of customer inquiries.
The Tint & Coating Identifier is, in a sense, the public version of an internal customer-service decision tree that a glass manufacturer's technical team had been refining for decades before I joined them. The framework is sound. The tool is the framework, in software, for the homeowner who does not have a manufacturer's technical-service line to call.
Identify the substrate. Then clean. The order is not negotiable, and the substrate identification is the part that took me a decade to internalize. The tool is the closest I can get to teaching it through a screen.
Easton Giordano is the contributing science editor at Window Washing Guide. He holds a PhD in materials chemistry from the University of Washington and spent eight years as a senior research chemist at a major architectural glass coating manufacturer in the Pacific Northwest before going independent in 2021. He now consults on glazing failure analysis and writes about the chemistry of glass for trade and consumer publications. He is, by his own admission, insufferable about vinegar.
Easton is the contributing science editor at Window Washing Guide. He holds a PhD in materials chemistry from the University of Washington and spent eight years as a senior research chemist at a major architectural glass coating manufacturer in the Pacific Northwest before going independent in 2021. He now consults on glazing failure analysis and writes about the chemistry of glass for trade and consumer publications. He is, by his own admission, insufferable about vinegar.