miscalculating volume

[JenBen]

Hi,

I'm new to soap making and tried to test out a new set of molds. They're silicone, so I filled them with water and emptied the water into a measuring cup. I came up with roughly 1 cup or 8 ounces for all 6 cavities per mold. I like them a bit full so I entered 16.50 ounces into soap calc. I used a recipe that recommends 20% superfat and a 2:1 ratio of water to lye for a 100% coconut oil soap. I came up with and measured out 4.84 ounces of water and 2.42 ounces of lye. I threw in a couple of dashes of cinnamon, just for fun. When I poured the soap it only filled 8 of the 12 cavities. What did I do wrong?

Jenifer

 

[The Efficacious Gentleman]

Hi!

There is a great and pretty much sure fire formula for working out the capacity of a container when it comes to soaping. Of course, there is a wee bit of a margin of error, but not much. Trouble is, I can't remember it! Will search and update......

 

[The Efficacious Gentleman]

Ah, it's stickied right at the top of this section! Or here as a link

https://www.soapmakingforum.com/threads/how-to-figure-how-much-oil-for-mold.2909/
Basically width X length X height of your mold (the inner part) X 0.4 if you're working in inches or 0.72 if using cm. That gives you your oil weight. Not including water and lye, just oil weight.

That's the margin of error - if I use a 40% solution and you use a 30% solution, there will be a difference in the amount of water we would use for the same recipe, so a difference in total volume. But it's not a huge amount, all told.

 

[Megan]

Weighing your water in the mold might be a better option if the mold is irregularly shaped (meaning not square, rectangular). Usually for irregular shaped molds, I will put it on the scale, tare, and fill one cavity with water. I go in grams but you could do oz because the density of water is 1 g/ml or 0.9587 oz/fl oz at room temp. Then I multiply my result by the number of cavities I have.

 

[JenBen]

Weighing your water in the mold might be a better option if the mold is irregularly shaped (meaning not square, rectangular). Usually for irregular shaped molds, I will put it on the scale, tare, and fill one cavity with water. I go in grams but you could do oz because the density of water is 1 g/ml or 0.9587 oz/fl oz at room temp. Then I multiply my result by the number of cavities I have.

 

[JenBen]

Thank you everyone.

The molds are irregularly shaped and as they are flexible, they really difficult to manipulate once filled with water.
I solved this problem by putting a mini (and rigid) cutting board under the molds and putting both on the scale to follow Megan’s suggestions. Whereas the first time I tried to weigh the amount and came up with ~450 grams, this time I came up with 490 grams.

Thanks again,

Jenifer

 

[Todd Ziegler]

Thank you everyone.

The molds are irregularly shaped and as they are flexible, they really difficult to manipulate once filled with water.
I solved this problem by putting a mini (and rigid) cutting board under the molds and putting both on the scale to follow Megan’s suggestions. Whereas the first time I tried to weigh the amount and came up with ~450 grams, this time I came up with 490 grams.

Thanks again,

Jenifer

Check out the description from where you bought the molds. Sometimes they list the capacity of each individual mold or as a whole.

When I have irregular molds and I can't find the capacity for the mold, I will use melt and pour soap to fill one cavity and then weigh it. That usually gives me an accurate idea of how much they will hold. Then I just save the MP for use later in another project or mold.