It is current opinion that glass fragments can serve as an ignition source for grassland, bush and forest fires by focussing sunlight. In order to check the validity of this assumption, ignition experiments were conducted in the open over six litter samples taken from forests in northern Germany. Of several glass fragments, the five bottle bottoms best focussing sunlight were installed 15–50 cm above the litter materials. We found that one bottle bottom was able to slightly char spruce needles, beech leaves and blades of grass. Although this particular bottle bottom let the temperature increase up to 327°C, flame formation did not occur. A secondary (but more realistic) experiment with a glass-bottle bottom lying on the litter led to a maximum temperature of 82°C in the space between the litter and the glass fragment.