Noticed the project presented by https://www.instructables.com/id/Concrete-Lamps/ in which he did a great job and I decided to create one myself (having some prior experience in concrete) with all the steps necessary, and I hope, very good steps for you to follow and mix with your own awesome creativity.

This project was very fun and it involved a lot of creativity. Also the materials used in this project are based on your personal taste. I love the combination between white cement and copper or a copper with an old patina. So its up to you what kind of cement, stone powder of even stone rocks, it depends on your taste and the size of the project.

Materials needed:

white cement
marble powder (for a smoother finish, not a rocky industrial one)
board polystyrene foam(minimum 5 mm thick) for the mold in which you pour the cement
copper pipe, copper fittings
copper rod and steel rod
copper wires or normal wires
duct tape or something similar
electric wires , light bulb, light bulb socket & all connecting stuff

Tools needed:

clippers
Dremmel tool or anything that can be use for sharpening a rod
knife
marker

Please use all the proper safety measure and enjoy:D

Step 1: Creating the Mold

First of all find a design or create your own and break it into parts(planes) that can be cut into the foam and combined into the mold for the concrete. Also remember a dense foam can hold curved shapes.

As you can see, in the first picture this was my idea for the project. In the second picture you can see the shapes that I cut into the foam board. The shapes are informative and not to scale. I made the picture to show you the pieces required.
Draw all the pieces on the foam and cut them out using a knife( 3rd to 7th picture)

Cut 2 cm long pieces from some toothpicks to help you on the next tricky part(2nd picture).
Using the cut toothpicks combine all the pieces except the ones on top. Those pieces will be added after the frame is inserted to give strength to the concrete. See the way I combined them in the next pictures (8th to the last).

After you combine them, use some duct tape or something similar and put it over the edges to give them strength so they can hold the cement in while it hardens.

Step 2: Creating the Frame and Finishing the Mold

As you can see I decided to make a simple frame that follows the curvature of the lamp.
Of course this can be made more intricate but for this project it will do.

Cut two steel rods or any type of rods which are at least 2 mm in thickness.
Measure the distance you need to place the rods inside of the mold without touching any part of it, except for the base which is not visible.

Use some copper or aluminum wires (because they are more flexible and you can shape them easily) and connect them like in the second picture. The aspect doesn't matter because these parts will be inside of the cement and are used purely for giving the lamp strength.

Insert this frame into the mold and add the remaining foam pieces to complete the mold. Also leave a gap on top so you can pour the cement through there.
Be careful when you insert the frame to sit inside of the mold without touching its walls so the wires or rods wont stick out of the cement and look bad.

See the result in the last picture.

Step 3: Adding Details

I decided to add 3 sharpened spikes on the left side of the lamp and a tube through the other for the wires to pass through.

For the spikes:
I used a copper rod because it has a nice look to it. This exact rod "helped" me with a flat tire. I was driving near a construction site and it entered, of course, without my permission into the tire. But I'm sure you will be able to find one in an old electric cable or at a specialized store.

Cut the rod into 3 ( one 7 cm, one 11, and one 15) and make them sharp using a Dremmel tool or something simmilar.
Insert them into the foam from the outside though to the interior of the lamp
See this process in the first 8 pictures.

For the copper tube:
I used 14 cm long and 8 cm long copper tube, 90 degree copper coupling and a copper cap. Drill a hole through the cap so you cand pass the wires.
See the 9th picture to the 13th for this process.

After that using this combine copper tube mark a spot in the inside of the lamp and a spot on the outside, cut them out and fit the pipe through.
See the remaining pictures for this process.

Step 4: Making the Cement Mix

In this step you will need:

white cement
marble powder (for a smoother finish, not a rocky industrial one)
bowl

Before starting, make sure you have a breathing mask, glasses and gloves because cement dust can be very irritating.

Find a can or a bowl in which you will prepare the mix.
The ratios I used were: 2 parts marble powder and 1 part cement.
The tricky part here is to put in the correct amount of water. Too much water and the concrete will harden slower and will retain water inside and will take a lot to harden, or may even break in time due to the water kept inside. Too less water and the concrete will be very hard to put inside the mold and will not bond properly and you will have air gaps. Probably the best consistency can be obtained by adding water a bit at a time, and stir until you get a toothpaste like consistency. Stir it very well!

After you make the paste put it in the mold using a cup.
Wile poring the concrete stop from time to time and hit the mold to a table or shake the mold so the concrete flows down and fills every empty space.

Leave it for 24 to 48 hours to harden in a place that's not too dry and definitely not hot or cold (about 18 to 25 ^oC will do). I left it for 50 hours just to be sure. Remove the mold.
Leave it to dry in open air for at least 3 days and from time to time rinse some water over the whole thing.

Step 5: Making the Whole Thing Purty' and Adding the Electrical Stuff

Get some sand paper, preferably fine one so you won't leave marks. If the concrete dust bothers you get some sand paper that can be used with water.

Sand all the ruff edges until you get a smooth finish. You can paint it if you want but the white look of the lamp is appealing and I think painting it will ruin the overall aspect. (pictures 1 to 8)

Before making the electrical stuff I observed that my light bulb socket was very hard to connect with the copper pipe. I got a 22-15 mm copper fitting and after that i sanded the bottom part of the socket until it was able to fit in the fitting. (picture 9 to 15)

Electrical stuff: