The Hesed L’Avraham, (Mysical work by R. Avraham Azulai, grandfather of the Rav Chida, Ch. 55), discusses various materials that a menorah should be made of. He lists them in the preferred order of hashivut.
3. Golden Bronze
11. Glazed Porcelain
12. New Unglazed Porcelain
13. Pomegranate Shell
14. Coconut Shell
15. Acorn Shell
Rav Shlomo Zalman Orbach (Renowned Posek, 20th Century Jerusalem) was asked: If a person has a silver menorah but uses glass cup inserts for the oil-is that considered silver or glass? Does a person lose the high-level hidur of silver because of the convenience of glass? Rav Orbach answered that since that is the normal way to use a silver menorah, the glass is batel to the silver, and therefore it is considered silver.
Another issue that arises today is the pre-filled solid oil cups. Does the coagulating agent added to the oil render the oil unfit for lighting? Rav Elyashiv (Renowned Posek, 20th Century Jerusalem) ruled that it is permitted since the coagulant is less than one sixtieth of the total oil; it is batel b’shishim.
Rabbi Bitan in the Yalkut Yosef (p.118) brings an interesting proof that coagulated oil is permitted. He quotes the Teshuva Me’Ahava who claims that the oil that they found in the times of the Hashmonaim was solidified oil. Halachically, it had to have a status of "food" and not "liquid". If it was used in the Beit HaMikdash, then clearly we can use it.
SUMMARY: Using class inserts in a silver menorah is considered a preferred level of beautifying the misva. It is permitted L’Hathila to use coagulated oil for lighting.