Photo Engineer

12-25-2008, 08:37 PM

I have commented before on the fact that old emulsions used active gelatin and therefore are not truly usable without some sort of conversion with modern inactive gelatin.

Here is a handy hint that is different from using sulfur or sulfur + gold to get the same results as the old timers.

I've equated temperature with speed. Up in temp, up in speed. I've also equated addition time with contrast (and to an extent speed) in that up in addition rate, up in contrast.

These two general rules can allow one to convert an emulsion from the old style to the new style with minimum pain and still use modern gelatins. The trick is to raise the temperatures and decrease the addition times used in a formula.

Here is an example. Let us assume a formula uses 5' addition of Silver Nitrate at 40 deg C and then a digest of 20 minutes at 50 degrees C. To convert, a hint would be to add the Silver Nitrate over 2.5' at 50 deg C and digest 20 minutes at 60 degrees C. This is just a hint of a starting point, but you get the picture that time and temperature can be used to "adjust" a formula for use today and it is possible to omit the sulfur sensitization step otherwise needed for increasing speed and contrast when using refined gelatins.

Just a handy tip. You will have to play with your formula to get what you want out of it, but here is how you start.

PE

Here is a handy hint that is different from using sulfur or sulfur + gold to get the same results as the old timers.

I've equated temperature with speed. Up in temp, up in speed. I've also equated addition time with contrast (and to an extent speed) in that up in addition rate, up in contrast.

These two general rules can allow one to convert an emulsion from the old style to the new style with minimum pain and still use modern gelatins. The trick is to raise the temperatures and decrease the addition times used in a formula.

Here is an example. Let us assume a formula uses 5' addition of Silver Nitrate at 40 deg C and then a digest of 20 minutes at 50 degrees C. To convert, a hint would be to add the Silver Nitrate over 2.5' at 50 deg C and digest 20 minutes at 60 degrees C. This is just a hint of a starting point, but you get the picture that time and temperature can be used to "adjust" a formula for use today and it is possible to omit the sulfur sensitization step otherwise needed for increasing speed and contrast when using refined gelatins.

Just a handy tip. You will have to play with your formula to get what you want out of it, but here is how you start.

PE