Sunshine is used to bleach all mat straws, but more often they are also treated with boiling water to which certain bleaching agents have been added. Only the most important of these are explained.

Tamarind.—This tree (Tamarindus indica) is known in Tagalog, Bicol and Pampanga as sampalok, in Visayan as sambag, in Ilocano as salamagui, and in Palawan as kalampisao. It is a large tree with dense foliage. The leaves are employed as a bleaching agent in boiling water. It is said that the young green fruit can be used for this purpose.

Pandakaki.—The leaves of the plant (Tabernaemontana pandacaqui) are used as a bleaching agent. This is the name under which it is known, particularly in Pampanga and Cavite. In Palawan it is called alibetbet. It is also known as kampopot in Tagalog and as alibubut and toar in parts of the Visayas. In Ilocano the name is kurribuetbuet.

Lemons.—The juice of the various species and varieties of Citrus is employed to some extent for bleaching. It is usually added to boiling water in which the straw is immersed.

Vinegar.—Of Philippine vinegars, those made from palm juices are considered about half as strong as lemon juice. Vinegar from sugar cane juice has probably the same strength. That made from cooked rice is considered about one-fourth as strong as lemon juice.

Alum.—In some towns alum is added to the boiling water in which straw is treated. It is usually employed in combination with other bleaching agents.