Resources
Low-Iron Glass — What It Is, and When a Mirror Actually Needs It
Standard mirror glass has a faint green cast. Most of the time nobody notices. Here is where it starts to matter.
Short answer: ordinary float glass contains iron oxide, which gives it a faint green cast. Low-iron glass is made with a reduced-iron batch, so the cast largely disappears. On a mirror the difference shows most on the exposed edge and across large or joined panels; on a small framed mirror it is usually invisible.
Where the green comes from
The sand used to make float glass carries iron oxide as a natural impurity. It is what gives a cut sheet that familiar green line along the edge. Looking through the face of a thin pane you barely see it; looking along the edge, or through a thick panel, you see it clearly.
A mirror doubles the effect, because light passes through the glass, reflects off the silver and passes through again. So a mirror shows more colour cast than a window of the same substrate.
Low-iron glass — sometimes sold as ultra-clear or extra-clear — uses a batch with the iron content reduced. It is a different raw material, not a coating or a treatment applied afterwards.
Where it shows, and where it does not
| Situation | Does the difference show? |
|---|---|
| Small framed mirror, edge concealed | Rarely |
| Polished or bevelled exposed edge | Yes — the edge is where the cast concentrates |
| Large single panel | Yes, across the field |
| Panels butted together in a wall | Yes, and side-by-side comparison makes it obvious |
| Against white or very pale finishes | Yes — white reads as slightly green |
| Behind a tint (grey, bronze, champagne) | No — the tint dominates |
The last row is worth noting because it saves money. If the design calls for a tinted mirror, low-iron substrate underneath it is usually wasted spend.
What it does not do
Low-iron glass is a clarity choice, not a performance one. It is not stronger, it does not change the safety backing class, and it does not change whether a panel can be tempered. Those are separate specifications and none of them follow from choosing low iron.
It also does not affect the silvering itself. A copper-free coating and a low-iron substrate are independent choices — you can have either, both or neither, and they solve different problems: copper-free addresses edge corrosion in humid rooms, low-iron addresses colour.
When we would recommend it
Where the edge is exposed and polished, where panels sit adjacent, where the surrounding finishes are white or very pale, and on any large single panel. On small framed pieces, on tinted work, and where the mirror is concealed behind a cabinet door, standard float is usually the sensible choice.
Our rounded rectangle copper-free low-iron project mirror combines both substrate choices for wet commercial areas, and the round copper-free high-humidity mirror covers the round format.
Asking for it on a purchase order
Write the substrate into the specification rather than assuming it. "Low-iron" or "ultra-clear" on the line item, plus the thickness, is enough — and ask for a sample if the room has pale finishes, because the difference is easier to judge against the actual wall colour than from a description.
The specialty mirror range covers the copper-free and low-iron builds. Send the panel sizes and the finishes around them, and we will come back within 24 hours.