A turbah (Arabic: تربة; Persian: مهر mohr) is a small piece of soil or clay, often a clay tablet, used during salat (Islamic daily prayers) to symbolize earth. The use of a turbah is compulsory in most Shi'a schools of Islam and many Hadith mention the benefits of prostration (Sajda) upon the soil of the earth or an alternative material. The most favoured soil is that of Karbala, the site of the death of Husayn ibn Ali; however, soil from anywhere may be used.
It is permissible to prostrate on a clay on which something is written, though it is much better to prostrate on plain clay ( Torbah) or Mohr or Sajdagah.
According to Shia jurisprudence, Sajda should be performed on earth, and on those things which are not edible nor worn, and on things which grow from earth (e.g. wood and leaves of trees). The Holy Prophet (pbuh) also performed Sajda on soil and other things which are considered to be a part of earth such as sand, clay, stone, plants (wood) etc. not on carpet, rug, leather and plastic materials. The Turbah of Imam Hussein (a.s.) on which Sajda is valid and which has superiority over other soils and things, is one of the manifestations of earth (or soil). Hence, Sajda is allowed on it.
So in this case, you will prostrate on the epoxy, not the Turbah and the prostration on that, even if it's transparent and thin does not suffice.
No because epoxy would be a barrier between you and the thing which is permissible to do sajdah on.
If there is a layer that has formed on the turbah which is a barrier that stops the forehead from reaching the clay, then it must be cleaned or scraped away first
Thank you for your question. As long as the darkness is not due to any barrier between the turbah and the forehead you can prostrate on it. Usually, the darkness is due to water or swear and so the darkness is just discolouration of the clay rather than a barrier.
May you always be successful
Thank you for your question. You can bury them or throw them into a river if they have one of the Names of Allah or the Infallibles (as) on them. Throwing them in the rubbish may be considered desecration.
May you always be successful.