Nine coins can be weighed several times to obtain different qualities.

The concept of two hands, I think, refers to whether the two sides have the same mass when the number of coins held by the left and right hands is the same, so I give the solution for three times as follows.

The first time, left hand: 3, right hand: 3.

This is divided into two situations.

1. If both hands weigh the same, the left and right ***6 coins are standard coins. Then one of the remaining three coins is not a standard coin. Let these three coins become ABC ... for the second time, both hands are AB, and if they weigh the same, C is a special coin. If it is different, the third time: the left and right hands are AC, and if it is the same weight, B is a special coin.

2. If the weights of the two hands are different, the coin on the heavy side is ABC, the coin on the light side is DEF, and the remaining three coins must be standard coins, that is, XXX: the second time: the left and right hands take ABC and XXX respectively. There are two situations here.

(1)ABC is heavy, so one of ABC is special currency, and the special currency is biased. At this time, you can choose two coins (such as A and B) to compare their weights. The heavier coin is a special coin. If the quality is the same, the third coin is a special coin.

(2) If the weight is the same, a DEF coin is a special coin, and the special coin is lighter. At this time, you can choose two coins (such as A and B) to compare their weights, the lighter one is a special coin, and if the quality is the same, the third one is a special coin.

Simply put-first take out a coin, then take four coins in one hand, see which one is heavy, and put down the other five coins; Take two coins in each hand, which side is heavier, and then take off the two coins in one hand and the coins in the other hand are lighter. This is a special coin.