Dilute aqua regia

...Also, if you need to react with the sample for a long time, it is more efficient to dilute it twice as much with water before using it. This is called dilute aqua regia. Generally, the solution dissolved in aqua regia treatment still has oxidizing power even if it is diluted, so it is easier to use a reducing reagent next time by heating it while adding sulfuric acid or hydrochloric acid to drive out the nitric acid.

*Some of the terminology that refers to "dilute aqua regia" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…また試料と長く反応させる必要がある場合は，水で倍に薄めて使うほうが効率がよい。これを希王水と呼ぶ。一般に王水処理で溶解した溶液は薄めても酸化力が残っているから，硫酸あるいは塩酸を加えながら熱して硝酸を追い出しておいたほうが，次に還元性の試薬を用いる場合などに操作がしやすい。…

※「希王水」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報