How to Make Asphaltum Varnish

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The same asphalt used to make roads dissolves in turpentine to make varnish.
The same asphalt used to make roads dissolves in turpentine to make varnish. (Image: Jupiterimages/Comstock/Getty Images)

Asphalt, also known as asphaltum, is used in varnish form as a resist for acid etching, blacking for wrought iron or as a dark varnish and sealant for wood. Asphalt dilutes readily in turpentine. When an asphalt-turpentine mixture is applied to a surface, the turpentine evaporates, depositing a layer of smooth asphalt on the desired surface. You can purchase both asphalt and turpentine at a hardware or home-improvement store. Make sure to buy pure asphalt and not an asphalt mixture. The finished product will be thick but can be diluted to the desired working consistency.

Things You'll Need

  • 2 woven canvas bags
  • 5-gallon bucket, with lid
  • 25 cups asphalt
  • 3 gallons of turpentine

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Select two canvas bags so that each will fit inside a 5-gallon bucket like a garbage bag. After putting one of the bags in the bucket, you should be able to pull the sides of the bag over the edges of the bucket and lift the bag eight inches off the bottom of the bucket.

Place one bag inside the other and hold the ends together.

Add the asphalt to the doubled bag.

Pour the turpentine into the bucket.

Place the doubled bag containing the asphalt into the bucket. The turpentine will seep through the bag and cover the asphalt.

Fold both bags over the edge of the bucket and adjust the bags until they are eight inches off the bottom.

Hold the bags in place and secure the bucket lid. The lid will hold the bags above the bottom of the bucket and allow the asphalt to dissolve into the turpentine.

Allow the asphalt to dissolve for three to four days.

Lift the bag from the asphaltum varnish and allow the liquid to drain. Any insoluble asphalt particles will be trapped inside the bag.

Stir the varnish thoroughly before use to ensure an even distribution of the asphalt throughout.

Transfer the varnish to another container and dilute it with more turpentine to achieve the desired consistency for each project.

Tips & Warnings

  • Never dilute stock varnish in the stock container.

References

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