As in an earlier instance, I am just sharing information and am not concerned much with whether the information would fit a particular pre-modern text exactly.

On Nov 26, 2015, at 6:02 AM, Dominic Goodall <dominic.goodall@gmail.com> wrote:
Bearing these guiding principles in mind I was in favour yesterday of understanding mṛtsnā as “steatite/chalk pencil” or the like, and therefore perhaps simply as “writing implement” generically.  I certainly still think that this is possible, but I now think that the “powder” hypothesis (chalk, talk, or, as N. Ganesan has suggested, turmeric) cannot be abandoned either. 

There used to be a writing implement called dhüḷ-pāṭī धूळपाटी in Marathi (which would correpond to धूलि-पाटी or धूलि-पट्टि/पट्टी  ‘dust-board’ in Skt and hence will be relatable to mṛtsnā). I have not seen one and am not entirely sure about the extent to which it was used or the exact way in which it was used. However, it was definitely used to learn writing and was associated with texts that were not meant to be preserved. Students probably wrote numbers, alphabet letters and practice sentences on it and corrected or erased the writing after the teacher had checked it for accuracy. Perhaps the following publication, which I cannot access at present, will have more information about it: Sarma, S.R. 1985. Writing Material in Ancient India. Aligarh: Viveka Publishers. Aligarh Oriental Series, No. 5.  

a.a.