My Second Lampshade Form:

My second lampshade form was for a pair of lamps that weren’t quite as wide or as flat as my first lampshade form.  My requirements were pretty much the same.

My 19” Ikea commercial lamps

Making my mold:

I started out to make my mold exactly the same way that I did the first time.  When I went to buy a large piece of Styrofoam, I didn’t find exactly what I was looking for.  Instead I found the packages of green Styrofoam bricks that they use for arranging flowers.  When I started to shape the Styrofoam, I made a happy discovery.  I discovered that, by rocking my wood profile back and forth on the pivot point, I could use the edge of the profile to chop and scrape the Styrofoam to exactly the right shape. 

I’ll have more about this later.  This is one of the key elements in my new process.  I was so set on my plaster mold objective that I failed to realize that a Styrofoam mold might work just as well.

I made two missteps at this point:

First, I read on the plaster of paris container that, if I wanted a longer work time, I should use plaster wall patch.  Using plaster wall patch changed the dry time from 30 minutes to days.

Second, I hoped to get away with the lack of a gap between my wood profile and the Styrofoam.  I guess that I was hoping that the plaster wall patch would simply fill in the voids and pores in the Styrofoam.  What it did do was make an awful mess.

I cleaned up the mess and thought about cutting or rasping the surface of the Styrofoam to get the necessary clearance under the wood profile.  Instead, I attached a couple of small blocks to the profile and raised it 1/4 inch.  From there, applying the plaster of paris proceeded exactly as before.

Mold for my second lampshade form

Making my lampshade form:

Time for another misstep.  I had been thinking long and hard about what I might use in place of the papier-mache and how I might avoid having to fiberglass the outside.  I had an inspiration.  Why not use spray foam sealant (the stuff that dries hard rather than the softer stuff that they put around doors and windows).  It would take pins and it would be rigid enough to not need the fiberglass.

After putting Saran wrap on my mold, I covered the mold with foam sealant.  After letting it dry overnight, I removed it from the mold.  It was certainly rigid enough but I found that the foam sealant set so fast that it left a lot of voids.  The work surface, which needed to be smooth, was full of voids.

My second lampshade form

 This wasn’t a total loss.  I had discovered a simple substitute for the fiberglass.  I recast my lampshade form, once again using the papier-mache mix from the craft store.  Once it dried, I covered the outside with foam sealant.  Worked great.

Spray foam sealant underside