Venus daan is given on Friday: rice, sugar, white cloth, silver. Charity addresses a graha without amplifying it, which is why it is prescribed where a gemstone is withheld.
Daan is charity aimed at a specific graha, given on its day and matched to its significations. Classically it is the remedy that works when a gemstone would be dangerous — it addresses the planet without amplifying it, which is why it is prescribed for Rahu and Saturn where stones are withheld.
Venus charity is white sweets, rice, white cloth and silver, given on Friday — classically to married women, widows and arts education.
A weak Venus shows as difficulty in marriage, restless dissatisfaction, and money that goes on pleasure. The remedies steady the relationship rather than the bank balance.
Friday. Fasting, charity and mantra japa for Venus all belong to that day.
The mantra, the weekday fast and the charity are safe for anyone — they address Venus without amplifying it. Diamond is not: a planetary gem strengthens whatever the graha is already doing, so it needs a chart reading first.