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There is this:
Gyatrul Rinpoche in "The Generation Stage in Buddhist Tantra (with thanks to Dorje):
Padmasambhava, says: "The best type of mala to use to increase the number of recitations is a mala made from some type of precious jewel (Tib. Tin O che). A mediocre type of mala is made from the seed of a tree or fruit, and inferior type of mala is made from wood, earth, stone or medicine."
A mala made from seashells, earth, wood or seeds from trees or fruit is meant to be used to accomplish peaceful sadhanas and peaceful action. A mala made from gold will accomplish expansive karmas. A red coral mala is best for accomplishing powerful sadhanas. A steel or turquoise mala is good for wrathful activity. A mala made from dzi or other precious stones can be used to accomplish any of the karmic activities you are doing.
A mala made from apricot stones will accomplish expansive activity. A mala made from "lot ton" (a tiny, round black seed within a fruit) accomplishes powerful activity A mala made from raksha beads accomplishes wrathful practices. A mala made from bodhi seeds accomplishes all dharmas. Malas of bodhi tree wood accomplish peaceful karmas. A mala of mulberry beads accomplishes powerful karmas. Malas of mahogany wood accomplish wrathful practices. Malas made of ivory, especially from an elephant's tusk, will accomplish all concerned activity.
Beads made of stone are good for expansive practice. Beads made of medicine are good for wrathful practice. Malas with many different types of jewels are good for any practice. However, I suggest that you not attempt to create a mala with a lot of different beads on it because, unless you know which combinations are effective, you may cause a non-positive result.
Next, the text mentions the different kinds of benefits that are derived from using different types of malas. An iron or steel mala multiplies the virtue that is accumulated with each recitation in a general way. A copper mala multiplies each recitation four times. A raksha mala multiplies each recitation by 20 million, and a pearl mala by 100 million. A silver mala multiplies by 100,000 and a ruby mala by 100 million. A bodhi seed mala manifests limitless benefits for any form of practice, be it peaceful, expansive, powerful or wrathful.
You should all know the mala's meaning and the best way to string it. String your mala using three, five or nine strings, and no other number. Three strings symbolize the three kayas, five strings symbolize the five buddhas, and the nine strings symbolize the nine vehicles.
The main guru bead may be composed of three beads, symbolizing the three vajra states of being, the three kayas. The smallest bead on the outside should be blue, perhaps made of lapis. The color blue symbolizes the unchanging mind of ultimate truth. The bead in the middle should be red, to symbolize vajra speech, and the innermost bead should be white, to symbolize the vajra body.
Your mala must be blessed by a lama, and you should constantly bless your mala yourself by imbuing it with energy. You must put energy into your mala before counting recitations with it, to produce real benefit.
You should clean your mouth and hand, and then your mala, before using it. You may also scent it with sandalwood oil.
Next, generate yourself as the deity, place the mala in your left hand and arrange the beads with the guru bead placed vertically in the center. Recite the mantra that transforms all dharmas into the awareness of their true nature: OM SWABAVA SHUDDO SARVA DHARMA SWABAVA SHUDDO HAM. This mantra cleanses and transforms impure perceptions into the awareness of emptiness.
From emptiness, the guru bead appears as the central deity in the mandala, and the other beads appear as the members of the entourage. This part of the practice is the meditation upon the samayasattva. Next, invoke the jnanasattva. Invite the primordial wisdom beings to come forth, hooking them so that they dissolve into the samayasattva, just as you would in a sadhana. Invite the wisdom beings to come from their pure lands into the space in front of you. They then dissolve into your mala and remain firm there. Thus, every part of your mala is the entire mandala. This includes the central deity, entourage, lotus seats, ornaments, hand emblems, colors, etc. Blessing your mala in this way multiplies each syllable of whatever mantra you then recite 100,000 times, besides causing good karmic results. Therefore, it is extremely important to do this.
Your mala represents not only the form of the deity but the speech of the deity as well. For example, if you recite the One-HundredSyllable mantra, the guru bead represents the syllable OM and the other beads represent the remaining syllables.
Guru Padmasambhava said, "Whenever you recite peaceful mantras, use the tip of your thumb to count the mala. When reciting expansive mantras, use the third finger. Use the ring finger and thumb when reciting powerful mantras, and use the little finger when reciting wrathful mantras." Use only your left hand to count mantras. The right hand is but rarely used; for instance, in some wrathful practices. Some books teach the use of both hands, but do not use the right hand only.
Whatever kind of practice you are doing, whether peaceful, wrathful, powerful or expansive, always be aware that the thumb is a vajra hook which hooks spiritual powers, deities and other blessings. It is also easy to move the beads with your thumb.