Revelations (v6.7) patch introduced alchemy in Viron, which can transmute "useless" items into potentially valuable items like Dragon Heart and Symbol of Naraka. See [v6.7 Feature] Alchemy for a list of possible drops, and Alchemical Materials for a list of ingredients available in v6.7.
The following test was done with three Grade 3 alchemical ingredients, then upgraded by adding more vis. The total rank is thus 10 (3+3+3+1), costing 198,000 vis. This was done 116 times at a total cost of 22,968,000 vis. The results are as follows:
I got 1 Symbol of Naraka out of 116 refinements. The most common drop was 10 Hermes Potions (25/116), followed by 3 HQ Gems (20/116) and 3 Rough Stones (19/116).