Heavy cotton or linen saturated with linseed oil becomes translucent, passes about 60% of light and must be re-oiled every year, which makes it a workable last resort when no glass or plastic is available. Linseed-oil-soaked cloth can heat itself and catch fire when piled or crumpled while drying, so hang it open and never store oily scraps in a heap.
Part of Glazing Options
Oiled cloth and thin animal membranes are traditional translucent coverings used before glass became cheap.
Oiled Cloth Is A Fallback With A Fire Hazard Attached
Before affordable glass, growers and builders covered frames with cloth made translucent by oil. The method still works: heavy cotton or linen soaked in linseed oil lets through about 60% of light, against about 90% for glass. It sheds rain, but needs re-oiling each year, and the oil takes time to dry. It is a viable choice only when nothing better is at hand.
The hazard is real. Linseed oil dries by reacting with oxygen, and that reaction gives off heat. Spread thin on a hung sheet, the heat escapes into the air. Bunched or piled while still wet, it can build up faster than it escapes and ignite the cloth.
What You Need
- Heavy cotton or linen, closely woven
- Linseed oil
- A frame to stretch it on (see Frame Materials: Wood, Bamboo, Salvage)
- A place to hang the cloth open, outdoors or in a draughty shed, away from buildings
- A bucket of water for oily scraps
Method: Oil, Dry And Fit The Cloth
Step 1: Stretch the cloth on the frame. Pin it flat so it is not creased or folded.
Step 2: Apply oil in thin coats. Work the oil into the fibres by brush or soaked cloth until the cloth turns translucent. Several thin coats beat one drenching one.
Step 3: Let each coat dry hung open. Never bunch, fold or stack the wet cloth. Keep it spread in moving air until the surface is no longer tacky.
Step 4: Handle oily rags safely. Put every oily rag, brush wipe and offcut into a bucket of water, or spread it flat outdoors to dry before disposal. Do not leave them in a pile or in a closed container.
Step 5: Re-oil each year. Light transmission and waterproofing fade. Re-oil on the frame and repeat the safe-drying rules.
Animal Membranes
Thin scraped skins, gut and bladder membranes, and parchment-like sheets can pass diffuse light and were used for small windows. They come only in small pieces, rot in persistent damp, and are best treated as stopgap panes for a cold frame or a vent rather than a greenhouse covering. Parchment Making describes preparing scraped skins. No light-transmission figure is given here because none is sourced; hold a sample up to the sun and compare it with oiled cloth before committing a frame to it.
Common Mistakes
- Piling wet cloth — this is how fires start. Keep it spread.
- Keeping oily rags in a closed tin — the heat stays in the tin.
- Putting oiled cloth near a stove — it is flammable even when dry.
Safety
Spontaneous ignition of oil-soaked cloth
Drying oils such as linseed oil release heat as they cure. Wet cloth in a heap, a bundle or a closed container can ignite without any flame, sometimes hours after the work is done. Hang cloth open to dry, wet scraps in water, and never store a pile of oily rags inside a building.
What’s Next
- Learn next: Glazing Options — compare the choices
- Combine with: Climate Control — keeping the interior stable behind a dim covering