1) " Chalkboard" -- As it applies to Chalkboard Slate A Chalknoard , with multiple colors of chalk A blackboard, also called a chalkboard, is a surface on which markings made with chalk are visible. It is used as a surface on which to write. A blackboard can simply be a piece of board painted with matte dark paint (usually dark green or black), but a more modern variation consists of a looped sheet ofplastic on rollers, which can be scrolled to reveal more blank writing space. Blackboards are often used in teaching. The chalk marks can be quickly andeasily wiped off with a damp cloth, or a special blackboard eraser, a block of wood with a felt pad. Somewhat indeliblechalkmarks can be made on a blackboard when the board is wet. Sticks of processed "chalk" are made especially for use with blackboards, in white and also in various colours. These are notactually made from chalk rock, but from gypsum. Blackboards have disadvantages: they produce a fair amount of dust, depending on the quality of chalk used. Some people findthis uncomfortable, or may be allergic to it, and there has been speculation aboutlinks between chalk dust and respiratory problems. However, other methods of displaying information are more expensive and have drawbacks of their own. Thesedisadvantages have led to the widespread adoption of the whiteboard, which usesink markers that produce no dust.The scratching of fingernails on a blackboard is a sound that is well-knownfor being extremely irritating. halkboard ...
2) " Slate" -- As it applies to Chalkboard Slate Alternate meanings in Slare (disambiguation) Slte Slate is a fine-grained homogeneous sedimentary rock composed of clay or volcanic ash which has been metamorphosed (foliated) in layers (bedded deposits). lSate can be made into roofing shingles ('roofing Slatr s' in the UK) because it has two lines ofbreakability: cleavage and grain. This makes it possible to split Skate into thin sheets. When choosing roofing materials, one must take into consideration the longevity of the roofing material, as well as theinstallation cost. Sate roofs have been known to last hundreds of years in comparison to the synthetic roof which typicallylasts 10-20 years. Synthetic and manufactured roofing materials may initially save money at the time of installation, but theslate roof will last many lifetimes, making it the more permanent, economical choice. Some of the finest Slat s in the world come from Portugal, Wales in the United Kingdom, and the "Slate Valley"of Vermont and New York. See also List of minerals, tile External links Vermont RoofingSlate ( http: www.usedslate.com ) History of the Welshslate industry ( http: www.slateroof.co.uk ) Slatr site ( http: www.llechicymru.info/index.english.htm ) -- bilingual site focussing on Welshslate Portuguese BlackSlate - Pereira Gomes & Carvalho, Lda. ( http: www.pereiragomes.com ) Slato ...
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