Scripts

arts = {
[1] = {mass = 1},
[2] = {mass = 14},
[3] = {mass = 7},
[4] = {mass = 8},
[5] = {mass = 11},
}

function GetRandomArt()
  local sum
  local n
  for id, props in arts do
    sum = sum + props.mass
  end
  n = random(sum)+1
  local start, finish, shift = 0, 0, 0
  for id, props in arts do
    finish = start + props.mass
    if start<=n and n<finish then
      return id
    else shift = finish-start
         start = finish
         finish = start+shift
    end
  end
  return 0
end

You can also manually create a table of 95 elements (not necessarily all of them), specifying a weight for each — the higher the weight, the greater the chance of it dropping.