Stained glass pattern maker

How to make a stained glass pattern from a photo

1. Open the photo. One clear subject with big shapes works best: a flower, a bird, a house, a pet's head, a landscape with three or four bands. Slide Crop position to keep the part you want; the photo is cropped to the panel's shape.
2. Type the panel size in cm or inches, measured to the centre of the outside lead.
3. Choose the glass. 3 to 16 colours, taken from the photo. Tap a swatch in the key to pick your own colour instead, for example the sheet of glass you already own.
4. Simplify. Smallest piece merges every piece under that area into its closest neighbour; Smoothness rounds off ragged edges and speckle before the pieces are drawn; each step is a 1.5 mm wider majority filter at panel size, so it does the same on a small panel and a big one. The summary line counts the pieces as you go.
5. Fix the red pieces. Red means hard to cut. Raise the smallest piece or the smoothness, or tick Auto-split to cut the red pieces with straight lines.
6. Print it. Print the PDF at Actual size (100 %), check the 10 cm line with a ruler, and tape the tiles together on the overlap lines. Cut two copies: one to keep whole as the layout, one to cut into pattern pieces.

How the cutting check works

Glass does not cut like paper. A score runs straight or in a gentle curve and the glass breaks along it from edge to edge, so some shapes cannot be broken out in one piece however careful you are. The check looks at every piece on the working grid (800 pixels on the panel's long side, so about 0.5 mm a pixel on a 40 cm panel) and flags three things:

• An inside curve sharper than the limit. For each dent in the outline (a place where the outline bends into the piece) the page takes the straight line across the dent's mouth and the dent's deepest point; the angle at that point between the two ends of the mouth is the inside angle. A shallow dent is close to 180°; a half-circle bite is 90°; an L-shaped piece's inner corner is about 90° too. The default flags anything under 110°, about a dent deeper than a third of its width. Dents shallower than 3 mm are left to the grozing pliers and not flagged.
• A neck narrower than the limit. Where a piece pinches between two wider parts, the break tends to run through the pinch. The default is 10 mm (about 3/8 in). A piece that is narrower than the neck width everywhere is merged into its neighbour before the check, because it is a sliver rather than a piece.
• A piece that surrounds another. Glass cannot be cut round a hole, so a ring needs at least one cut.

Auto-split cuts the red pieces with straight lines, one cut at a time. Each cut is one straight line across the piece: from the deepest point of one of its three sharpest failing dents, heading into the piece (within 60° of straight in), or across a neck, or right through a hole, tried every 5°, shortest first. A cut is only kept if every part is at least the smallest piece size and no part is narrower than the neck width everywhere. The first cut after which every part passes wins; if none does, the cut that leaves the least flagged glass (area times how badly it fails) is made, and any part that is still red gets the next cut, up to 8 cuts per original piece. A piece that straight cuts cannot fix stays red, and the line under the preview says how many; split those by hand on the printout, or relax the limits.

Worked example: a crescent moon 18 cm tall whose hollow is a bite out of a 15 cm circle. The check measures the hollow's inside angle at about 86°, so the crescent is outlined in red. Auto-split cuts it from the bottom of the hollow straight across to the outer edge, a cut about 5 cm long; the two halves' hollows then measure about 129° and 136°, and both pass.

Lead came, copper foil and line width

The line you see is as wide as the came's face or the solder seam on the finished panel, so a small piece shows how much of it the lead will cover. A 1/4 in came is 6.35 mm wide: on a piece 2 cm across, that is about a third of the visible glass. The print draws that width as a grey band with a thin black centre line; cut along the centre line with pattern shears made for lead or foil, which take out the narrow strip the came's heart or the foil needs.

What it cannot do

• It cannot promise a piece will not crack. The check is a guide built from the shapes alone; it does not know your glass (streaky and textured glass breaks less predictably), your cutter or your break. A piece that passes can still run the wrong way.
• Flat panels only. It does not make lamp shades, boxes or 3-D patterns, and it does not plan the outer border came or a frame.
• Screen colours are not glass colours. Glass is seen with light through it, and the same sheet looks different against a north window and a lamp. Use the key to choose colours, then pick the real sheets in daylight.
• It does not draw a design for you. The lines follow the colour areas of your photo. A busy photo makes many small pieces; a tight crop of one subject makes far better glass than a wide scene.
• Waste is an allowance, not a measurement. 25 % is a common rule of thumb; grain direction, streaks and awkward shapes can need more.
• Your work is kept on this device only. Another browser or a private window starts empty, and clearing the browser's site data deletes it.

Questions

Is this stained glass pattern maker free and printable?

Yes. There is no account, no watermark and no limit. The PDF prints the pattern at the panel's true size over as many A4 or Letter pages as it needs, with a colour key and glass list page; the SVG holds the lines for a cutting machine or a drawing program.

How do I turn a photo into a stained glass pattern?

Open the photo, type the panel size in cm or inches, and choose how many glass colours (3 to 16) and the smallest piece in square centimetres. The preview shows the panel with the lead at its real width. Pieces outlined in red are hard to cut; raise the smallest piece, add smoothness, or tick Auto-split, then print the PDF at Actual size.

What makes a stained glass pattern good for beginners?

Few, large pieces with gentle curves. Glass breaks along a straight or gently curving score, so deep inside curves, L-shaped pieces, narrow necks and pieces that surround another piece are where beginners crack glass. This tool outlines those in red. For a first panel of about 30 × 40 cm, aim for 20 to 40 pieces: 4 to 6 colours and a smallest piece of 15 to 25 cm² usually get there.

How much glass do I need for a stained glass pattern?

The glass list gives each colour's area in cm² and square feet, measured to the centre of the lines, and adds a waste allowance you set (25 % by default, a common rule of thumb rather than a measurement). Grain, streaks and the shape of the pieces can need more, so buy generously for the colour with the biggest pieces.

Can I make a pattern for copper foil instead of lead?

Yes. Choose copper foil and the lines are drawn 2 mm wide, about a neat soldered seam, or type your own width. Lead came is drawn at its face width: 3/16, 1/4, 3/8 or 1/2 inch (4.76, 6.35, 9.53 or 12.7 mm), so you can see before cutting how much of a small piece the lead will cover.