Article: Toothpaste contains microscopic abrasive particles that can polish and grind down the exterior layers. Again, do not use any fabrics that are coarse or abrasive on their own; they will leave additional scratches in the lens. Do not use circular motions as they can create circular scuff marks. The abrasives in toothpaste are harsher than microfiber cloth alone. Concentrating on a single area for too long could penetrate the exterior layers and damage the interior lens. You can use warm water or glass cleaners, or a combination of the two. Remove any remaining smudge marks from fingers or traces of residue from the toothpaste.
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Apply toothpaste to the scratched lens. Use a piece of soft fabric to rub the toothpaste over the lens. Rub the toothpaste over the lens using a side-to-side motion. Wash off the toothpaste. Perform a final cleaning with a microfiber cloth.

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Use a coffee can or similarly shaped container as your quenching chamber. Pour in water or vegetable oil so it's 23 inches (5.17.6cm) from the rim of the container. Make sure the oil or water is at room temperature. This step should be done before heating the steel, as the steel should be quenched immediately after removing from heat. {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/1\/1a\/Harden-Steel-Step-4-Version-3.jpg\/v4-460px-Harden-Steel-Step-4-Version-3.jpg","bigUrl":"\/images\/thumb\/1\/1a\/Harden-Steel-Step-4-Version-3.jpg\/aid1214287-v4-728px-Harden-Steel-Step-4-Version-3.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class="mw-parser-output"><p>License: <a rel="nofollow" class="external text" href="https:\/\/creativecommons.org\/licenses\/by-nc-sa\/3.0\/">Creative Commons<\/a><br>
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<\/p><\/div>"} Water is great for rapidly quenching the hot metal, but it could cause thin steel to distort or crack. Vegetable oil has a higher boiling point, so the hot steel will take longer to cool and reduce the chance of it cracking. However, oil may spill and create a fire hazard if the steel is put into the oil too quickly. The water or oil will continue to boil as the heat transfers from the steel. Keep the steel completely submerged until there is no more steam or bubbles, which should only take a few minutes. Set the steel back on your work surface when you're finished.
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One-sentence summary --
Fill a heat-safe container with water or oil deep enough to submerge your steel. Remove the steel from the quenching medium when it stops bubbling.