Lithothanography: A How-To guide

[Sir Farthington-Smythe]

Lithothanography involves converting a photograph into a plate of light-translucent material of varying topography, which, when back-lit, reveals a stunning replica of the original photograph.  Lithothanes work by varying the amount of light passing through a translucent material in order to produce hues and shades, which intern reveal a photograph.  In this how-to guide, I will attempt to walk you through the process of creating a lithothane using a source photograph of your choosing.  For this guide, you may choose to follow along with the same photograph I provide, or use one you already have in mind.



What you need:

• A 3D printer or 3D printing service
• A digitized source photograph
• Cura V 2.4 or above
• Blender v2.74 or above

SELECTING A SOURCE PHOTOGRAPH
Unfortunately, not every photograph is suitable for lithothanography.  The source image must have a decent contrast ratio.  Images which are overly dark or overly bright without varying degrees between bright and dark willl not produce good results.

For this exercise, I shall be using this photograph, sourced through Google.


1) Open Cura


2) Open your source image, or simply click and drag your source image into Cura


3) Enter Lithothane settings
Upon opening or dragging in your source image, the following dialog will appear.  The three settings with which we need be concerned are:

• Height (mm): 3
• Base (mm): 1
• Darker is higher

After entering and accepting the values, Cura will analyze the image to create the basis for our lithothane.


Once it finishes slicing, choose File -> Save All -> Save to file
In the file dialog that appears, change the Save as type: to STL File (Binary)(*.stl), and enter a filename.  In this example, we shall name the file, lithothane.stl.

4) Prepare the lithothane model
Launch Blender

Hit Esc to remove the splash screen.
Tap the A key on your keyboard twice to select everything.
Tap X and hit Enter to clear the entire scene.
From the menu, choose File -> Import -> Stl (.stl)
Browse to the lithothane.stl file we created in step 3.
Once imported, the lithothane object will be quite large, so use Shift-C to centre and zoom the viewport.


5) Prepare the Lithothane object
Currently, our lithothane is laying flat on its back.  We want it standing vertical, so tap the R key on your keyboard, then type x90 and hit enter.  This will rotate our litothane to the correct orientation.


Hit Tab to enter edit mode.  The object will turn yellow, as every single vertex is highlighted.
Use Ctrl-[numpad_1] to switch to back view.
Then hit [numpad_5] to switch to orthographic view.
While everything is still selected, hit the Remove Doubles button on the left-hand tool panel.  This will ensure that we are dealing with a single mesh.
Now go into face editing mode by pressing the Face select button at the bottom of the viewport.
Right-click one of the two back faces to select it, then Shit-Right-Click on the other face to add it to our selection.


With both of these faces selected, hit X and select Faces from the pop-up menu.
With these two faces removed, the entire object looks black, because there are a lot of tiny faces which make up the detail of our lithothane.


Hit [numpad_3] to switch to the right side view.


Use Shift-middle-mouse-button to bring the top to the centre of the viewport and scroll_wheel to zoom in.


Go into vertex editing mode by selecting the Vertex select button at the bottom of the viewport.
Hit Z to enter x-ray mode.


Hit B, then click-drag a selection box around the top row of vertices to select them.


Go back into Face editing mode the same way we did before.  This will select all faces on the top of our lithothane.


Hit F to merge these into a single face.


Hit A to deselct everything, then return to vertex editing mode.
Use Shift-middle-mouse-button to bring the bottom edge of our Lithothane into view.


As before, use B then click-drag a box to select the bottom row of vertices.


Return to Face edit mode.


Merge the faces by hitting F.


Hit A to deselect everything, then return to vertex editing mode.
Hit [nubpad_7] to switch to top view.  Use Shift-C to centre the viewport.
Using the same technique as before (Shift-middle-mouse-button for scrolling, and scroll_wheel for zooming, bring the right edge to the centre of the viewport.


Use the same process as before to select the right-most column of vertices.


Switch to Face edit mode.


Merge the faces, same as before (Hit F).


Deselect everything and return to vertex editing mode.
Repeat these steps for the left-most column of vertices...





Deselct everything and return to vertex editing mode.
Zoom out and centre on the entire top of our Lithothane.


Select the entire back row of vertices.


Hit X, then select Limited Dissolve from the pop-up menu.
This will remove the extra vertices between the four corner vertices.


Use Ctrl-[numpad_1] to enter back view, and then Shift-C to centre and zoom.
With the four corner vertices still selected, hit F to form a face joining the four vertices.


Activate Edge editing mode by clicking the Edge select button at the bottom of the viewport.


Use Shift-Right-Click to, one at a time, deselect the left and right edges, leaving the top and bottom edges selected.


On the left-hand tool bar, hit the Subdivide button.  This will split the back face into two faces.


We need more than two faces to produce a good curve, so on the left-hand side near the bottom of the tool panel, change Number of Cuts to a value of 510.  This will create 512 vertices along the top edge joining 512 respective vertices along the bottom edge.  This will give our back face enough faces for a smooth curve.


Use the middle-mouse-button to rotate the view around to the front of our model.  Hit A a few times until everything is selected.


Use Ctrl-N to normalize all the faces (i.e. make them all face out).  Then hit Tab to exit editing mode.


Rotate the object 180 on the z-axis (hit R, then type z180 and hit Enter).


Use Ctrl-A and select Rotation from the pop-up menu.  This sets the current rotation values to zero, and puts our model into the required orientation for adding the curve.
Go back to top view ([numpad_7]).


Just in case you accidentally left-clicked at some point and moved the 3D cursor, hit Shift-C to put it back to centre.
Hit Shift-A and select Curve -> Circle from the pop-up menu.
Adjust the radius using the slider (left tool panel, at the bottom), until the circle is roughly as wide as the lithothane model.


Right-Click the Lithothane object to select it.


Add a curve modifier.  Look for the wrench tab on the attributes panel on the right.  Select the Curve modifier from the drop-down list of modifiers


Under Object, select BezierCirlce.


This tells our object to conform to the curve.  Use the middle-mouse-button to rotate the view around to the back.  Even though we refined the back, it looks like a bunch of flat faces forming a low-res circle.  To refine the curve, right-click the circle, then activate the curve tab on the properties panel on the right.  Change the Preview resolution to 512.


Right-click the Lithothane object to select it.  Activate the object modifiers tab (the wrench), and click the Apply button.  This will permanently apply the curve to our model, so that it becomes independent of the bezier circle itself.


Right-click to select the bezier circle.


Hit X, then Enter to delete the curve.
http://brownrigg.ca/images/project-steampunk/lithothanes/How-to/Lithothane-step48.png

Right-click the Lithothane object to select it.
Use the menu bar to select File -> Export -> Selected -> Stl and find the location where lithothane.stl was stored. Name the file lithothane-curved.stl to distinguish it from the original STL file.

We are done with Blender at this point.  For those of you who do not have their own 3D printer, send your lithothane-curved.stl to your preferred 3D printing service.  For those of you who do have your own 3D printer, keep reading.

5) Slice the model
If you still have Cura open from before, clear the build plate (Edit -> Clear Build Plate)


Open lithothane-curved.stl


Here is a list of settings that I found produce a good result when printing lithothanes.  I normally print in 1.75mm polylactic acid.  You may need to adjust your settings accordingly, but these are a good start.

Quality

• Layer Height: 0.2mm
• Initial Layer Height: 1.4mm

Shell

• Wall Thickness: 0.8mm
  
  
  • Wall Count: 2
• Outer Wall Wipe Distance: 0.2mm
• Top/Bottom Thickness: 0.8mm
• Top/Bottom Pattern: Lines
• Outer Wall Inset: 0mm
• Compensate wall overlaps: Yes
  
  
  • Outer: Yes
  • Inner: Yes
• Fill gaps between walls: Everywhere
• Horizontal Expansion: 0mm
• Z Seam Alignment: Shortest
• Ignore Small Gaps: Yes

Infill

• Density: 100%
  
  
  • Line Distance: 0.4mm
    
• Pattern: Lines
• Overlap Percentage: 0%
• Skin Overlap Percentage: 5%
  
  
  • Skin Overlap: 0.02mm
• Infill Wipe Distance: 0.1mm
• Infill Layer Thickness: 0.2mm
• Infill Before Walls: Yes

Material

• Printing Temperature: 195°C
• Build Plate Temperature: 50°C
• Flow: 100%
• Enable Retraction: Yes
• Retract at Layer Change: No
• Retraction Distance: 0.8mm
• Retraction Speed: 35mm/s

Speed

• Print: 60 mm/s
• Infill: 60 mm/s
• Travel: 120 mm/s
• Initial Layer: 30 mm/s

Cooling

• Enable: Yes
• Fan Speed: 100%
• Regular/Maximum Fan Speed Threshold: 10s
• Initial Fan Speed: 0%
• Minimal Layer Time: 5s

Support

• Enable: No

Build Plate Adhesion

• Type: Skirt

There ya go.  Hopefully you were able to follow along, and now have your very own lithothanes.  I have yet to print the one made in this example, but when I do, I shall post it here.  If you do happen to make your own lithothanes, I would like to see them.  It would be interesting to see how the results from using the same image and following the same steps might produce consistent results.

If you are having trouble with any of these steps, let me know, and shall endeavour to assist.

[Peter Brassbeard]

If you have openscad https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Other_Language_Features#Surface can convert an image.  But I haven't found a way with that app to bend the surface.

[Antipodean]

Magnificent How Too.
That would have taken you a while.
Thank You for sharing.

[Sir Farthington-Smythe]

Magnificent How Too.
That would have taken you a while.
Thank You for sharing.

I am pleased you enjoyed it. It did indeed take a while to write it up, but was also a pleasure to share my experience.