I put a string as a value for a material and it didn't work. What's wrong?

So my friend Max loves to script, so I made this model for him. This is the only script inside and there is something wrong. The problem is at Line 26. I need help figuring it out!

local function newpart()
    local boss = script.Parent.Parent --The model that the script is inside

local newPart = Instance.new("Part", game.Workspace)
newPart.Position = script.Parent.Parent.PlaceHolder.Position


newPart.Anchored = false
--So that the part falls out of the machine
local x = math.random(1,7)
local y = math.random(1,7)
local z = math.random(1,7)
newPart.Size = Vector3.new(x,y,z)
boss.SizeX.SurfaceGui.TextLabel.Text = "Size: "..x..", "..y..", "..z
--Size
newPart.BrickColor = BrickColor.Random()
boss.BrickColorX.SurfaceGui.TextLabel.Text = "Color: "..newPart.BrickColor.Name
--Color
local tr = math.random(100,1000)
tr = tr / 1000
newPart.Transparency = tr
boss.TransparencyX.SurfaceGui.TextLabel.Text = "Transparency: "..newPart.Transparency
--Transparency
local m = math.random(1,21)
local ml = {"Brick","Cobblestone","Concrete","CorrodedMetal","DiamondPlate","Fabric","Glass","Granite","Grass","Ice","Marble","Metal","Neon","Pebble","Plastic","Sand","Slate","SmoothPlastic","Wood","WoodPlanks"}
local mlm = ml[m]
newPart.Material = mlm
boss.MaterialX.SurfaceGui.TextLabel.Text = "Material: "..mlm
--Material
local s = math.random(1,3)
if s == 1 then
    newPart.Shape = Enum.PartType.Block
    s = "Block"
elseif s == 2 then
    newPart.Shape = Enum.PartType.Ball
    s = "Ball"
elseif s == 3 then
    newPart.Shape = Enum.PartType.Cylinder
    s = "Cylinder"
end

boss.ShapeX.SurfaceGui.TextLabel.Text = "Shape: "..s

wait(10)

local newTool = Instance.new("Tool")

newTool.CanBeDropped = true
newTool.Name = "Part"
newPart.Parent = newTool
newTool.RequiresHandle = true
newPart.Name = "Handle"
newTool.Parent = game.Workspace
newTool.ToolTip = s..", Color: "..newPart.BrickColor.Name..", Size: "..x..", "..y..", "..z
end

while true do
    newpart()
end

The problem is not in Line 25, the line just got cut off because of limited space.