This article, Lava Release, contains content taken directly from our mother site. All credit of such content is reserved the original authors over at Narutopedia, the original article can be read here: "Lava Release" .
When Raizo Ozunu's Lava Release is first referred to, the kanji 熔, with the radical for "fire" (火), is used. In later references when Shoji Kengen's is used, the kanji 溶, with the radical for "water" (水), is used instead. When both Chikara Shima and Rayoto Uzumaki used it, it was once again with the fire radical. This seems to indicate that the Lava Release from Kirigakure and Takigakure uses the water radical, while the Lava Release from other nations use the fire radical. However, in the data and fan books, both kanji have been used to refer to Raizo's Lava Release.
Nowadays, the two kanji are synonyms and used interchangeably, with 溶 being the more common variant. However, there seems to be a subtle difference in meaning between the two. The kanji with the fire radical seems to be used more often in words relating to metal and other solids, whereas the kanji with the water radical is more often used in words relating to liquids.
All of Rayoto Uzumaki's lava release techniques (excluding the lava release armor and clone techniques) use the tiger hand seal. A hand seal commonly used in fire release techniques.