Lamp Mk III

Continued with the MK III lampshade on Thursday.

First I cut down the cardboard tube to a more reasonable length before draping the silicone former perched on top of it with a 55cm x 55cm square of resined cloth.

It stuck to itself in a number of places, so I laid it out again on my large silicone mat and let it dry for a couple of hours. It was also sticking to the cardboard tube, so I wrapped that in a thin silicone mat.

Tried again, but it was still sticking to itself within the flutes. I therefore laid it out on the silicone mat again and gave both sides a coating of spray oil. This solved the problem, but the corner points of the cloth square were not perfectly aligned. While 2 corners were aligned perfectly on a concave flute, the two remaining corners were slightly, but not disastrously, misaligned.

What I forgot to do was give the cloth a 2nd coat of resin.

Measuring the cloth and locating the exact centre is crucial to correct positioning, but precisely positioning a piece of cloth covered in resin is extremely difficult. I didn't persevere, as this one too is a demo piece from which I'm learning.

Yesterday morning I was greeted with an almost perfectly formed lampshade, although it was not as stiff as I would have liked, due to the lack of a 2nd coat.

Getting the spray cooking oil off was a small nightmare but, once washed off, I painted a reinforcing coat of resin over the exterior - nearly wasting a paintbrush in the process, but managed to get it off with hand sanitizing alcohol. Not ideal - what I really need is a water soluble, non-stick spray.

Had a go at making a resin mold for another liquid silicone former, using the existing silicone former as the template.

A perfect copy, but it was a bugger to remove. Had to use a lot of oil and finger power to get the original out of the resin.

I then cut a hole in the bottom of the shade, sat it in a deep coaster mold (to increase the stability with additional weight) and filled it with resin. 

Here's the finished product with no other source of illumination other than the LED display stand under it. The thickness of the resin base diffuses the light a bit too much and perhaps I should have sacrificed some of the weight to thinness to enable the shade to better capture the light. Paint the top and sides silver, perhaps? A proper base with an electric lightbulb in it would ramp up the power, but I'm leaving that for the Mk IV or Mk V,

I haven't yet tried using the woven fibreglass matting, but I suspect it will hold a lot more resin than the thin cotton I've thus far been using, so it might not require two coats of resin.

Lessons? Cover everything the shade could feasibly come into contact with in silicone. Rather than the sheet of silicone matting around the cardboard tube, I may smear it with caulking silicone. Next time, I may allow the sheet of resined cloth to dry almost completely and then use a heat gun to form it around the silicone former when dry. Spray cooking oil is great for preventing things sticking together, but not so easy to remove after the fact.