A mixture of a cellulose derivative and a liquid diluent is prepared which comprises at least 5 weight percent of the cellulose derivative, based on the total weight of the cellulose derivative and the liquid diluent. The mixing operation causes air to be entrapped in the mixture. The time for at least partially removing entrapped air is reduced by providing a cellulose derivative having a specific surface area of less than 0.20 m2/g measured by a BET method for preparing the mixture.