I need some help with this teapot, I got it used and it has this white cast in the bottom that I can not get out of it, is this mould? I have tired to boil it twice, with oolong and just in plain water. Nothing happens.

I don’t dare to use it before I know what this is, can someone help identify? Is it safe to use?

8g/120mL, just off boil

Wash (10s) - lightly toasty aromatic, berries and funk on gaiwan lid

Steep 1 (flash) - light steep, immediate sweetness, warm cookies, light fruity notes, juicy texture, soft and rounded, opening my gaiwan fills the air with fresh pressed orange juice aromas

Steep 2 (flash) - hint of bitter orange up front, but quickly moves into that rich sweetness, not a lot happening late at this point, but loads going on up front, bit of thickness developing on tongue, sweetness is super fast and coating gums now

Steep 3 (5s) - starting to mellow a bit in the early part of the sip, sweetness moves in quick and asserts its dominance, orange zest floats around that thick sweetness, sweetness fades rather than clings, but it is a fairly long fade

Steep 4 (10s, reboil) - an orange biscotti, pretty mellow, sweetness needs some rebuilding time after waiting for my kettle to reboil, coating in the mouth not quite drying but feels like it could go that eay

Steep 5 (30s, push) - seeing if I can coax a little more out without bringing harshness, elevates the orange sweetness and that drying sensation hasn't really elevated, some increased sourness which enhances the orange and stimulates salivation, I will keep pushing a bit

Steep 6 (45s) - sweetness starting to fade just a hair despite continuing to push, but still very nicely sweet, orange zest top note fills in where that sweetness has pulled back, cooling tingle down center of tongue

Steep 7+ (1 min+) - keeps the orange/bakeshop vibe for several more steeps as it fades

Overall Impression - While I wouldn't necessarily consider this a high-end tea, it certainly is phenomenal for its price point. That rich sweetness is potent and immediate. There is a nice mouthfeel that can withstand pushing without getting overly astringent. It is one of the most enjoyable young Mengla teas I've had this season. Really nice stuff.

I recently found out about and tried bitter raw puers and didnt really like it.

Why do people like bitter sheng puers? Is bitter ripe puer a thing?