Eyeball half of the 1/4 teaspoon, then eyeball half of that amount again. Alternatively, use a pinch, which is generally considered to be about 1/8 teaspoon.
When you need to divide a small dry ingredient measurement and don't have the exact measuring spoon, approximation is key. Here's a breakdown of methods:
The Halving Method: This involves visually dividing the original measurement in half, and then halving it again. In your case, you need 1/8 teaspoon, and you have a 1/4 teaspoon measure. First, fill the 1/4 teaspoon measure. Then, visually divide the powder in half. You now have approximately 1/8 teaspoon. If you need half of that, divide the 1/8 teaspoon in half again. This method relies on your visual estimation skills, so try to be as precise as possible.
The Pinch Method: A 'pinch' is a common kitchen measurement, often considered to be roughly equivalent to 1/8 teaspoon. To use this method, simply pinch a small amount of the ingredient between your thumb and forefinger. This is less precise than the halving method, but it's a quick and easy alternative.
Using a Knife: If you have a flat surface and a knife, you can spread the 1/4 teaspoon of ingredient into a thin, even layer. Then, visually divide the layer into four equal parts. Each part will represent approximately 1/16 teaspoon. Combine two of these parts to get your 1/8 teaspoon.
For critical ingredients like baking powder or baking soda, it's always best to invest in a full set of measuring spoons, including 1/8 tsp and 1/16 tsp measures, to ensure accurate results in your recipes. Inaccurate measurements of these ingredients can significantly affect the final product.