Rock Candle Design Basics

Rock Candle Design Basics
See link below to buy component starter kit)

Over the last two years an interest in making oil candles out of rock, glass, brick, ceramic and other masonry like products has caught on strong. This article is a primer on the subject matter offering answers to some of the more basic questions. 

Lets cover the reason why someone would want a "rock" candle, then cover the materials, then we will go into construction and some of the typical problems encountered.

"Rock" candles are decorative oil candles. They are a modern version of oil lanterns. Generally you have two categories, First being indoor oil candles and the other type for outdoors. The outdoor type is referred to as garden / patio oil candles. These oil candles are very attractive and fit most decor and landscapes. The colors are "earth tones" and the construction is a combination of stone, glass, metal, ceramic and other materials.

Materials: The classic "rock" candle is literally made of a smooth stone that is drilled out in the middle with a masonry bit. The volume that is drilled out is in relation to how big the rock is. Since rock is somewhat porous it is a good practice to set a glass vial or container in the rock so the fuel oil does not leach through pores and fractures in the stone. 

After the stone is drilled and a glass bottle or vial is set in the stone, usually some other material like slate is placed over the opening with a small drilled opening to accommodate a glass wick tube and wick.

Another concept is to drill a hole or holes in a piece of slate then attach it to a glass bowl or glass circular ash tray that will hold the fuel oil.

Another concept is to drill out a regular brick or glass brick and again set a vial or bottle to hold the fuel oil then cover it with a slate top to accommodate the wick tube and wick and also to cover the fuel cavity.

For simplicity I am going to make the easiest of the group. That is a drilled piece of slate over a glass bowl. Remember, you could also use a flat glass ash tray type bottom for the fuel "tank", but I want to exaggerate the features for teaching purposes. I am just trying to show basic design principles, not win any art awards. The material will include a 10 x 10 inch roof slate that has some nice weathering characteristics, a glass bowl, a glass (thermal) wick tube with a flared end to hold a fiberglass wick. I like fiberglass wicks because they last longer than cotton based wicks.

First I drilled a hole in the middle of the slate to accommodate a thermal glass wick tube and an additional hole for ventilation of the fuel. I will talk more on ventilation later. A good rule of thumb is to measure the wick tubes before drilling. In this case I am going to drill a large hole and support the glass wick tube with a brass grommet that you can buy at any hardware store. The larger hole makes it easier to refill the oil in the bowl below.

Next I will set the glass wick tube including the wick and support grommet. The tube length depends on the depth of the fuel bowl. The most often used size is 1.25" long measure below the flare on the tube. The diameter of the wick for indoor lamps should be from 1/16" to 1/8". In our case the wick tube will be part # TGWT-1.25 and the fiberglass wick will be part number #1284 (1/8"). Outdoor designs should use from 3/8" to 1/4". Wicks larger than that size go into the patio torch category that we will not discuss in this brief.

In this case, since the bowl is rather large I will just lay the slate over the bowl. Some folks attach the bowl to the slate using an automotive type adhesive that resists heat and the degradation that petroleum type products will cause. In our case that is the fuel. Remember, you can also use a flat glass ash tray as your fuel reservoir beneath the piece of slate. Actually the flat ash tray type looks better.

Regarding the fuel oil. I prefer the more refined version of liquid paraffin mainly because it has a high flash point, which is good for safety, and it burns cleaner. Before using any fuel read the instructions. Don't use gasoline or any fuel that will readily volatize !!!!!! You can find liquid paraffin at most hardware stores and some of the larger retailers. I like Lamplight Farms and Hollowick brands. Also, do your testing in an area that has sufficient fire protection, and have a fire extinguisher on hand. Our test lab has metal tables and two fire extinguishers nearby.

So our finished product is a piece of slate 10 x 10 inches square with two drilled holes. One for the wick tube and wick (TGWT-1.25 and 1/8" diameter fiberglass #1284-50) and the other for ventilation of the fuel in the bowl. The slate will set on top of a glass (I used Pyrex in this case) bowl. If you fear the bowl being knocked over then secure the slate to the bowl with an adhesive that is temperature and petroleum resistant. Next fill the bowl with the liquid paraffin by either lifting up the slate or using a funnel to pour the fuel through the wick tube port. Now you can see why I drilled a larger hole than needed for the wick tube and supported it with a brass grommet. Oh, by the way the grommets I chose are usually in the automotive section in most hardware stores. They are used to repair canvas tent and truck tarps. The size I have used is 3/8". It fits our series of tubes (e.g., "TGWT").

Now about the ventilation. This is very important. When you light a wick it creates a draw on the fuel to feed the flame. The larger the flame the more oil that is drawn into it (the flame) to sustain it. As the fuel oil comes up the tube it will create a vacuum in the fuel cylinder (in this case the bowl) unless there is a vent hole to equalize the air in the fuel cylinder. What happens is that the flame starts out strong and dies out in about 20 to 30 seconds. The usual reaction is that the fuel or wick is bad, which is not the case. Somehow air has to get into the fuel cylinder to account for the vacuum being created when the oil candle is burning. I drilled a larger vent hole than needed mainly for visibility in the photo. A vent as small as 1/32" will do.

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No warranties are expressed or implied from the above information. 

Sample Pack of Glass Tubes and Fiberglass Wick (Rock Candle Starter Kit) is Now Available Online.

If you are new to making oil candles and just want to test the waters as they say. Try a starter kit before investing in bulk purchasing.

Glass bowl for fuel reservoir. Circular glass ash trays look better. The bowl was used to emphasize the basics of construction.
Typical piece of roof slate. Notice drilled hole (1/2")  in middle and vent hole diagonally off to the lower left side.
Thermal glass wick tube (TGWT Series) holds the fiberglass wick. Note brass grommet adapter used to straddle drilled openings larger than the diameter of the flared collar. In our case the flare is about 3/8" diameter.
Thermal glass wick tube set in the slate opening. The tube is not "glued" into the slate. It just sits in the hole. Notice vent hole.
Close-up of Thermal glass wick tube. Now you can see the tube's flared top. This example I just drilled a hole a little bit larger than the shaft diameter of 7/32".
Fiberglass wick (#1284) installed in the thermal glass wick tube.
Side view of the oil candle with the slate set on the bowl. You could also glue it to the bowl with an automotive type adhesive.
Finished product. Note fiberglass wick coiled in the bottom of the bowl (aka fuel reservoir).

Slate or smooth flat rock for top.

Glass bowl, glass ash tray or the ultimate is to drill out a real rock or brick then set a vial or glass reservoir in the rock or brick. Cover the fuel cavity with a flat smooth rock or roof slate.

Thermal glass wick tubes "TGWT" 1.25 to 2 inch long for "deep" bowls and 0.75 inch for "short" bowls such as circular glass ash trays.

Grommets if you choose a larger drilled hole for the TGWT. Note the larger hole is also where you can re-fuel the oil lamp.

Fiberglass wick part number 1284-50 which is 1/8" diameter. Works for tubes 1.25 inch and longer. Use number 1376 for the 0.75 inch long tubes. Fold this wick in half so there are two "legs" sticking down in the oil.

Please note our wick tubes accommodate fiberglass wick part number 1284 straight and 1376 folded. For larger diameter wicks use flared metal tubes.

To see a more detailed description and the opportunity to buy the components.