Today I’m continuing my series of clay experiments with a category I’m calling the “heavy” clays—rhassoul and bentonite. These are the two heaviest”miscellaneous” clays I have, so I figured I’d pair them for this part of my investigation.

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Here are the questions I intend to answer about these clays:

  • What is the clay like? Does it seem heavy or fluffy, is it smooth or coarse? Does it have any distinctive scent? Is it uniform?
  • What is the colour like? How does it change when wet?
  • How dense is it? How much does 1 tbsp of the clay weigh?
  • How does it absorb water? How much water is required to turn 2 tsp of clay into a smooth paste that’s roughly the texture of cake frosting?
  • How does it hydrate? What is the consistency like when it’s been mixed with water?
  • How does it dry? How quickly, does it crack or peel?
  • How gentle or harsh is it on the skin? How does the skin feel after a mask made with the clay? (This question will obviously be somewhat objectively answered, but I’ll try my best to be consistent.)
  • Is there anything else worth noting?

This was my methodology:

  1. Weigh out one level tablespoon of each clay into a glass dish and note the weight in grams.
  2. Handle the clay and make notes on texture and colour.
  3. Weigh out 10g (2 tsp/10mL) of water into a glass dish and whisk in a little clay at a time until a thick, frosting-like texture was achieved. Note volume and weight of clay added.
  4. Apply a face mask of each clay and time how long it takes for the mask to feel tight. Note how it dries.
  5. Rinse off the mask and note how the skin feels afterwards.

Alright! Let’s begin.

Rhassoul clay

Rhassoul clay

Rhassoul clay, also known as Moroccan lava clay, is rich in silica, magnesium, potassium and calcium. It has a long history of use as a cleanser in and around Morocco, and is available in a variety of grains, from coarse to very fine. I’m using a relatively middle-of-the-road grain here: fine, but not too fine.

Bentonite clay

Bentonite clay

Bentonite clay (also called Montmorillonite) has a reputation as a strong cleansing and detoxifying clay. There are a couple kinds of bentonite, but the kind you’re most likely to get from your supplier is Sodium Bentonite (check to be sure), and that’s what I’ll be working with in these experiments. When hydrated the molecules become charged, which is why contact with metal is not advised—it interferes with this charge (don’t worry, you won’t get zapped, and contact with metal won’t harm the clay or make it harmful, it just makes it less effective).

What is the clay like? Does it seem heavy or fluffy, is it smooth or coarse? Does it have any distinctive scent? Is it uniform?
Both clays are heavy and sandy, and smell dusty—nothing too specific. The clays are uniform in particle size, but these particles are fairly large—like a finer sand.

Rhassoul clay—wet and dry

Rhassoul clay—wet and dry

Bentonite clay—wet and dry.

Bentonite clay—wet and dry

What is the colour like? How does it change when wet?
The rhassoul is a greyish brown, while the bentonite is quite grey. Both have some minor variations in particle colour, but nothing too striking. They both darken when wet.

How dense is it? How much does 1 tbsp of the clay weigh?
Both clays are quite dense. 1 tbsp of rhassoul clay weighs 15.7g, 1 tbsp of bentonite weighs 13.2g.

Rhassoul clay quickly settle sout of water in low concentrations.

Rhassoul clay quickly settle sout of water in low concentrations.

Bentonite clay loves to clump.

Bentonite clay loves to clump.

How does it absorb water? How much clay is required to turn 10g of water into a smooth paste that’s roughly the texture of cake frosting?
Rhassoul clay whisks into water easily (similar to how sand would), and settles out quickly, especially at lower concentrations. I used 2 tsp/7.1g of clay to turn 10g of water into a creamy cake-frosting like texture.

Bentonite clay is incredibly (and irritatingly) prone to clumping when combined with water. It’s crazy absorbent, so I only needed about ¼ tsp/1.5g for 10g of water. That’s SO little (about one tenth of how much French red clay you’d need for the same result)!

Rhassoul clay becomes a thick, slightly sticky paste when wet.

Rhassoul clay becomes a thick, slightly sticky paste when wet.

How does it hydrate? What is the consistency like when it’s been mixed with water?
Rhassoul clay hydrates up to a slightly tacky, vaguely peanut buttery paste. It’s fairly stiff, and definitely a bit gritty on the skin. It doesn’t spread onto the skin as easily or smoothly as the French clays do.

Bentonite is super weird when it gets wet—unlike any other clay. It’s crazy absorbent and turns water into a gelatinous type substance. You need to add it to the water just a wee sprinkle at a time, whisking with a wooden chopstick between additions. When hydrated, it’s like a slimy gel instead of a creamy, satiny paste like the French clays. It’s sort of like the gelatinous way oatmeal gets when it’s sat out for a while (appealing, eh?!). It spreads on the skin a bit like you might expect jello to—it takes some encouraging to get a somewhat uniform coating, and it’s translucent on the skin—the only clay I’ve found that is.

How does it dry? How quickly, does it crack or peel?
I found the rhassoul became tight and itchy pretty fast—I found it annoying by the 8 minute mark, and absolutely had to wash my face by 12 minutes. It became paler as it dried, but I couldn’t stand to have it on my face long enough to notice substantial cracking. It washed off easily.

Bentonite clay took a while to become itchy—about 15 minutes, with a 17 minute wash off point. As it dries you start to be able to see your pores as dark spots in the lighter, dried out clay, which is pretty cool. The clay becomes slimy and gel-like again as you try to wash it off, but it’s not too hard to get off.

Keep in mind that this is just clay + water; adding oil and other ingredients will change this.

How gentle or harsh is it on the skin? How does the skin feel after a mask made with the clay? (This question will obviously be somewhat objectively answered, but I’ll try my best to be consistent.)
Both clays left my skin feeling a pretty average post-mask dry. It wasn’t dry enough that I felt like I had to moisturize.

Is there anything else worth noting?
So—bentonite clay is super weird. The way it behaves with water is completely unique to any clay I’ve ever worked with. I’m often asked if bentonite is a suitable alternative to other clays, and if water is involved, the answer is a 100% no (not without major adjustments, at least). It’s sort of like using gelatin instead of flour. Weird, eh?

Rhassoul Clay Bentonite Clay
Weight per Tbsp (g) 15.7g 13.2g
Weight per Tbsp (oz) 0.55oz 0.47oz
Tsp of clay to 10g water 2 1/4
Clay to 10g water (g) 7.1g 1.5g
Clay to 10g water (oz) 0.25oz 0.05oz
Approximate ratio of clay to water (by weight) to make a smooth paste 7:10 3:20

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