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From BlenderWiki
Transparency
Mode: All Modes
Panel: Shading/Material Context Transparency
Materials in Blender can be set to be transparent, so that light can pass through any objects using the material.
Transparency is controlled using an "alpha" channel, where eachpixel has an additional value, range 0-1, in addition to
its RGB color values. Ifalpha=0, then the pixel is transparent, and the RGB values for the surface contribute nothing to
the pixel's appearance; for alpha=1, the surface is fully opaque, and the color ofthe surface determines the final color
ofthe pixel.
In Blender, there are three ways in which the transparency ofamaterial canbe set: Mask, Z-Buffer and Ray-trace. Each ofthese is
explained in more detail below. The Material Preview option with a
sphere object gives a good demonstration ofthe capabilities ofthese
three options.
Common Options
The following property controls are available for all transparency options:
Alpha
Sets the transparency ofthe material by setting all pixels in the alpha channel to the given value.
Fresnel
Sets the power ofthe Fresnel effect. The Fresnel effect controls how transparent the material is, depending on
the angle between the surface normal and the viewing direction. Typically, the larger the angle, the more opaque
a material becomes (this generally occurs on the outline ofthe object).
Specular-
Controls the alpha/fallofffor the specular color.
BlendControls the blending between transparent and non-transparent areas. Only used ifFresnel is greater than 0.
Mask
This option simply masks the Background. It uses the alpha channel to mix the color ofeachpixel on the active object
plane with the color ofthe corresponding background pixel, according to the alpha channel ofthe pixel. Thus for alpha
= 1, the object color is seen - the object is completely opaque; but ifalpha = 0, only the background is seen - the
object is transparent (but note that any other object behind the active object disappears).
This is useful for making textures ofsolid or semi-transparent objects fromphotographic reference material - a mask is
made with alpha opaque for pixels within the object, and transparent for pixels outside the object.
See Mask Trans arenc .
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The Transparency Panel.
Z Buffer
This uses the alpha buffer for transparent faces. The alpha value ofeach pixel determines the mix ofthe basic color of
the material, and the color ofthe pixel is determined fromthe objects/background behind it. Onlybasic settings are
available with this option; it does not calculate refractions.
Raytraced Transparency
Uses ray tracing to calculate refractions. Ray tracing allows for complex refractions, falloff, and blurring, and is used for
simulating the refraction oflight rays through a transparent material, like a lens.
Note that the RayTrace option is only available in the Blender Render and Cycles render engines, but not in the Game
Engine.
A ray is sent fromthe camera and travels through the scene until it encounters an object. Ifthe first object hit by the ray
is non-transparent, then the ray takes the color ofthe object.
Ifthe object is transparent, then the ray continues its path through it to the next object, and so on, until a non-
transparent object is finally encountered which gives the whole chain ofrays its color. Eventually, the first transparent
object inherits the colors ofits background, proportional to its Alpha value (and the Alpha value ofeach transparent
Material hit in between).
But while the ray travels through the transparent object, it can be deflected fromits course according to the Index of
Refraction (IOR) ofthe material. When you actually look through a plain sphere ofglass, you will notice that the
background is upside-down and distorted: this is all because ofthe Index ofRefraction ofglass.
Enable Raytracing
To get ray-traced transparency, you need to:
1. enable ray tracing in your Render settings. This is done in the Render context Shading Panel. Ray tracing is
enabled by default.
2. set your Alpha value to something other than 1.0.
3. in order for the background material to receive light passing through your transparent object, Receive
Transparent must be turned on for that material in the Material Shadow panel.
Options
In addition to the common options given above, the following property controls are
available:
IOR
Index ofRefraction. Sets how much a ray traveling through the material will
be refracted, hence producing a distorted image ofits background. See IOR
values for Common Materials below.
Filter
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Amount offiltering for transparent ray trace. The higher this value, the more
the base color ofthe material will show. The material will still be transparent but it will start to take on the color
ofthe material. Disabled (0.0) by default.
Falloff
How fast light is absorbed as it passes through the material. Gives 'depth' and 'thickness' to glass.
Limit
Materials thicker than this are not transparent. This is used to control the threshold after which the filter color
starts to come into play.Depth
Sets the maximum number oftransparent surfaces a single ray can travel through. There is no typical value.
Transparent objects outside the Depth range will be rendered pitchblack ifviewed through the transparent
object that the Depth is set for. In other words, ifyou notice black areas on the surface ofa transparent object,
the solution is probably to increase its Depth value (this is a common issue with ray tracing transparent objects).
You may also need to turn on transparent shadows on the background object.
Gloss
Settings for the glossiness ofthe material.
Amount
The clarity ofthe refraction. Set this to something lower than zero to get a blurry refraction.
Threshold
Threshold for adaptive sampling. Ifa sample contributes less than this amount (as a percentage), sampling
is stopped.
Samples
Number ofcone samples averaged for blurry refraction.
Examples
Index of Refraction
(Influence ofthe IOR ofan Object on the distortion ofthe background:
spheres ofWater, Glass and Diamond(top to bottom).). There are different
values for typical materials: Air is 1.000 (no refraction), Alcohol is 1.329, Glass is
1.517, Plastic is 1.460, Water is 1.333 and Diamond is 2.417.
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Influence ofthe IOR ofan
Object on the distortion ofthe
background: spheres of Water,
Glass and Diamond (top to
bottom).
Fresnel
16 pieces ofglass rotated in various directions demonstrate the angle-dependent Fresnel effect with ray-traced (left)
and alpha buffered transparency (right). Note that the major difference is the lack ofIOR effect in the latter case.
(Download .blend.)
Settings for Fresnel using ray-traced (left) and Z transparency (right).
Note the specular highlight in the F4 glass tile (which is facing midway between the light and the camera); the Fresnel
effect canbe seen in row C and column 6 where the faces are turned away fromthe camera.
The amount ofFresnel effect canbe controlled by either increasing the Blend value or decreasing the Alpha value.
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A simple scene with three glasses on a surface, and three lamps. Depth was set to 4, 8, 12, and 14, resulting
in render times of 24 sec, 34 sec, 6 min, and 11 min respectively. (Download .blend.)
Depth
Increasing Depth also considerably increases render time. Each time a light raypasses through a surface, the ray-
tracing algorithm is called recursively. In the example above, each side ofeach glass has an exterior and an interiorsurface. Light rays thus have to pass through four surfaces for each glass.
But not only that, at everypoint on a surface, some ofthe light can be reflected, or mirrored offthe surface in various
directions. This results in multiple rays needing to be calculated for eachpoint (often referred to as a tree ofrays[1]
(http://www.cs.unc.edu/~rademach/xroads-RT/RTarticle.html) ). In each ofthe rendered images above there are
640400=256 000 pixels. By increasing Depth, at least one tree ofrays is added to each pixel.
Be kind to your computer. Carefully placing objects in a scene to avoid overlapping transparent objects is often an
interesting alternative.
Hints
Transparent shadows
No transparent shadows No transparent shadows, environment lighting enabled
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Transparent shadows enabled, alpha set to 0.0 As previous, alpha set to 0.25
Transparent shadows with ambient occlusion set to
multiply, distance 1 (radius ofsphere)
As previous, distance increased to 2 (diameter of
sphere)
By default, the shadows oftransparent objects are rendered solid black, as ifthe object was not transparent at all. But
in reality, the more transparent an object is, the lighter its shadow will be.
In Blender, transparent shadows are set on the materials that receive the shadows fromthe transparent object. This is
enabled and disabled with the Receive Transparent button, in the Material context Shadow panel. The shadow's
brightness is dependent on the Alpha value ofthe shadow casting material.
Alternatives to transparent ray-traced shadows canbe found in the World context, namely the Ambient Occlusion,
Environment Lighting, and Gather panels. Alternatively, a texture canbe used to control the Intensity value ofthe
shadow-receiving material.
IOR values for Common Materials
The following list provides some index ofrefraction values to use when ray-traced transparency is used for various
liquids, solids (gems), and gases:
A
Acetone 1.36
Actinolite 1.618
Agalmatolite 1.550
Agate 1.544
Agate 1.540
Air 1.000
E
Ebonite 1.66
Ekanite 1.600
Elaeolite 1.532
Emerald1.560 -
1.605
1.560 -
J
Jade, Jadeite1.64 -
1.667
Jade, Nephrite 1.600 -1.641
Jadeite 1.665
Jasper 1.540
S
Sanidine 1.522
Sapphire1.757 -
1.779
Sapphire, Star1.760 -
1.773
Scapolite 1.540
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Alcohol 1.329
Alcohol, Ethyl
(grain)1.36
Alexandrite 1.745
Alexandrite 1.750
Almandine 1.83
Aluminum 1.44Amber 1.545
Amblygonite 1.611
Amethyst 1.540
Ammolite 1.600
Anatase 2.490
Andalusite 1.640
Anhydrite 1.571
Apatite 1.632
Apophyllite 1.536
Aquamarine 1.575
Aragonite 1.530
Argon 1.000281
Asphalt 1.635
Axinite1.674 -
1.704
Axinite 1.675
Azurite 1.730
B
Barite 1.636
Barytocalcite 1.684
Beer 1.345
Benitoite 1.757
Benzene 1.501
Beryl1.57 -
1.60
Beryl, Red1.570 -
1.598
Beryllonite 1.553
Brazilianite 1.603
Bromine (liq) 1.661
Bronze 1.18
Brownite 1.567
C
Calcite 1.486
Calspar 1.486
Cancrinite 1.491
Carbon
Emerald Catseye 1.605
Emerald, Synth
flux1.561
Emerald, Synth
hydro1.568
Enstatite 1.663
Epidote 1.733
Ethanol 1.36
Ethyl Alcohol 1.36
Euclase 1.652
F
Fabulite 2.409
Feldspar,
Adventurine1.532
Feldspar, Albite 1.525Feldspar,
Amazonite1.525
Feldspar,
Labradorite1.565
Feldspar,
Microcline1.525
Feldspar,
Oligoclase1.539
Flourite 1.434
Formica 1.47
G
Garnet, Andradite1.88 -
1.94
Garnet,
Demantoid
1.880 -
1.9
Garnet,
Demantoid1.880
Garnet, Grossular 1.738
Garnet, Hessonite 1.745
Garnet, Mandarin1.790 -
1.8
Garnet, Pyrope1.73 -
1.76
Garnet, Rhodolite1.740 -
1.770
Garnet, Rhodolite 1.760
Garnet,
Spessartite1.810
Garnet, Tsavorite1.739 -
1.744
Jet 1.660
K
Kornerupine 1.665
Kunzite1.660 -
1.676
Kyanite 1.715
L
Labradorite1.560 -
1.572
Lapis Gem 1.500
Lapis Lazuli1.50 -
1.55
Lazulite 1.615
Lead 2.01
Leucite 1.509
M
Magnesite 1.515
Malachite 1.655
Meerschaum 1.530
Mercury (liq) 1.62
Methanol 1.329
Milk 1.35
Moldavite 1.500
Moonstone 1.518 -1.526
Moonstone,
Adularia1.525
Moonstone,
Albite1.535
Morganite1.585 -
1.594
N
Natrolite 1.480
Nephrite 1.600
Nitrogen (gas) 1.000297
Nitrogen (liq) 1.2053
Nylon 1.53
O
Obsidian 1.489
Oil of
Wintergreen
1.536
Oil, Clove 1.535
Oil, Lemon 1.481
Oil, Neroli 1.482
Scapolite, Yellow 1.555
Scheelite 1.920
Selenium,
Amorphous2.92
Serpentine 1.560
Shampoo 1.362
Shell 1.530Silicon 4.24
Sillimanite 1.658
Silver 0.18
Sinhalite 1.699
Smaragdite 1.608
Smithsonite 1.621
Sodalite 1.483
Sodium Chloride 1.544
Spessartite1.79 -
1.81
Sphalerite 2.368
Sphene 1.885
Spinel1.712 -
1.717
Spinel, Blue1.712 -
1.747
Spinel, Red 1.708 -1.735
Spodumene 1.650
Star Ruby1.76 -
1.773
Staurolite 1.739
Steatite 1.539
Steel 2.50
Stichtite 1.520
Strontium Titanate 2.410
Styrofoam 1.595
Sugar Solution
30%1.38
Sugar Solution
80%1.49
Sulphur 1.960
Synthetic Spinel 1.730
TTaaffeite 1.720
Tantalite 2.240
Tanzanite1.690-
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Dioxide (gas) 1.000449
Carbon
Disulfide1.628
Carbon
Tetrachloride1.460
Carbonated
Beverages
1.34 -
1.356Cassiterite 1.997
Celestite 1.622
Cerussite 1.804
Ceylonite 1.770
Chalcedony1.544 -
1.553
Chalk 1.510
Chalybite 1.630
Chlorine (gas) 1.000768
Chlorine (liq) 1.385
Chrome Green 2.4
Chrome Red 2.42
Chrome
Tourmaline
1.61 -
1.64
Chrome Yellow 2.31
Chromium 2.97
Chrysoberyl 1.745
Chrysoberyl,
Cat's eye
1.746 -
1.755
Chrysocolla 1.500
Chrysoprase 1.534
Citrine1.532 -
1.554
Citrine 1.550
Clinohumite1.625 -
1.675
Clinozoisite 1.724
Cobalt Blue 1.74
Cobalt Green 1.97
Cobalt Violet 1.71
Colemanite 1.586
Copper 1.10
Copper Oxide 2.705
Coral 1.486
Coral1.486 -
1.658
Cordierite 1.540
Garnet, Uvarovite 1.74 -
1.87
Gaylussite 1.517
Glass 1.51714
Glass, Albite 1.4890
Glass, Crown 1.520
Glass, Crown,Zinc
1.517
Glass, Flint, Dense 1.66
Glass, Flint,
Heaviest1.89
Glass, Flint,
Heavy1.65548
Glass, Flint,
Lanthanum1.80
Glass, Flint, Light 1.58038Glass, Flint,
Medium1.62725
Glycerine 1.473
Gold 0.47
H
Hambergite 1.559
Hauyne1.490 -
1.505
Hauynite 1.502
Helium 1.000036
Hematite 2.940
Hemimorphite 1.614
Hiddenite 1.655
Honey, 13%
water content1.504
Honey, 17%
water content
1.494
Honey, 21%
water content1.484
Howlite 1.586
Hydrogen (gas) 1.000140
Hydrogen (liq) 1.0974
Hypersthene 1.670
I
Ice 1.309
Idocrase 1.713
Iodine Crystal 3.34
1.522 -
Oil, Orange 1.473
Oil, Safflower 1.466
Oil, vegetable
(50 C)1.47
Olivine 1.670
Onyx 1.486
Opal, Black 1.440 -1.460
Opal, Fire1.430 -
1.460
Opal, White1.440 -
1.460
Oregon
Sunstone
1.560 -
1.572
Oxygen (gas) 1.000276
Oxygen (liq) 1.221P
Padparadja1.760 -
1.773
Painite 1.787
Pearl 1.530
Periclase 1.740
Peridot1.635 -
1.690
Peristerite 1.525
Petalite 1.502
Phenakite 1.650
Phosgenite 2.117
Plastic 1.460
Plexiglas 1.50
Polystyrene 1.55
Prase 1.540
Prasiolite 1.540
Prehnite 1.610
Proustite 2.790
Purpurite 1.840
Pyrite 1.810
Pyrope 1.740
Q
Quartz1.544 -
1.553Quartz, Fused 1.45843
R
Rhodizite 1.690
1.7
Teflon 1.35
Thomsonite 1.530
Tiger eye 1.544
Topaz1.607 -
1.627
Topaz, Blue 1.610
Topaz, Imperial1.605 -
1.640
Topaz, Pink 1.620
Topaz, White 1.630
Topaz, Yellow 1.620
Tourmaline1.603 -
1.655
Tourmaline 1.624
Tourmaline, Blue1.61 -
1.64
Tourmaline,
Catseye
1.61 -
1.64
Tourmaline, Green1.61 -
1.64
Tourmaline,
Paraiba
1.61 -
1.65
Tourmaline, Red
1.61 -
1.64
Tremolite 1.600
Tugtupite 1.496
Turpentine 1.472
Turquoise 1.610
U
Ulexite 1.490
Uvarovite 1.870
V-WWardite 1.590
Variscite 1.550
Water (0 C) 1.33346
Water (100 C) 1.31766
Water (20 C) 1.33283
Water (gas) 1.000261
Water (35 C,
room temp)1.33157
Whisky 1.356
Willemite 1.690
Witherite 1.532
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Corundum 1.766
Cranberry Juice
(25%)1.351
Crocoite 2.310
Crystal 2.000
Cuprite 2.850
D
Danburite1.627 -
1.641
Danburite 1.633
Diamond 2.417
Diopside 1.680
Dolomite 1.503
Dumortierite 1.686
Iolite 1.578
Iron 1.51
Ivory 1.540
Rhodochrisite 1.600
Rhodonite 1.735
Rock Salt 1.544
Rubber,
Natural1.5191
Ruby1.757 -
1.779Rum, White 1.361
Rutile 2.62
Vivianite 1.580
Vodka 1.363
Wulfenite 2.300
Z
Zincite 2.010
Zircon1.777 -
1.987Zircon, High 1.960
Zircon, Low 1.800
Zirconia, Cubic2.173 -
2.21
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Category: Materials