The Bloom value or Bloom strength of gelatin is a measure of its hardness. For photographic and holographic purposes, a Bloom value in the range of 200-300 is common. Anything less than 200 tends to be too soft, and over 300, too hard. Most amateur holographers in the US use Knox brand gelatin (available at most grocery store) with good results. The following table gives the Bloom value for some readily available gelatins.
|Great Lakes (bovine)||225 seems to be the most commonly sold.|
|Great Lakes (porcine)||?|
|Knox||225 - 235|