diff --git a/README.md b/README.md
index d7f8683..9729f43 100644
--- a/README.md
+++ b/README.md
@@ -320,11 +320,25 @@ This creates a new metadata item of the specified type, name and value.
 
 This changes the value of an existing field, but will not change its type.
 
+You can't use `set()` to change core fields such as like `width` or
+`interpretation`.  Use `copy()` instead.`
+
+Image references will be shared by the operation cache, so modifying an image
+can chage an image somewhere else in your program. Before changing an image,
+you must make sure you own a private copy of an image with `copy`.
+
+```lua
+local new_image = image:copy()`
+new_image:set("orientation", 7)
+```
+
 ### `boolean = vips.Image.remove(image, field_name)`
 
 This will remove a piece of metadata. It returns `true` if an item was
 successfully removed, `false` otherwise. 
 
+As with `set`, you must use copy before removing a metadata item.
+
 ## Call any libvips operation
 
 You can call any libvips operation as a member function, for example
diff --git a/src/vips.lua b/src/vips.lua
index 77f5d7b..802df96 100644
--- a/src/vips.lua
+++ b/src/vips.lua
@@ -22,6 +22,7 @@ local vips = {
     vobject = require "vips.vobject",
     voperation = require "vips.voperation",
     Image = require "vips.Image_methods",
+    Image = require "vips.Interpolate",
 }
 
 function vips.leak_set(leak)
diff --git a/src/vips/Interpolate.lua b/src/vips/Interpolate.lua
new file mode 100644
index 0000000..359ee22
--- /dev/null
+++ b/src/vips/Interpolate.lua
@@ -0,0 +1,34 @@
+-- make image interpolators, see affine
+
+local ffi = require "ffi"
+
+local verror = require "vips.verror"
+local vobject = require "vips.vobject"
+
+local vips_lib = ffi.load(ffi.os == "Windows" and "libvips-42.dll" or "vips")
+
+local Interpolate = {}
+
+Interpolate.vobject = function(self)
+    return ffi.cast(vobject.typeof, self)
+end
+
+Interpolate.new = function(self)
+    return vobject.new(self)
+end
+
+Interpolate.new_from_name = function(name)
+    -- there could potentially be other params here, but ignore that for now
+    local interpolate = vips_lib.vips_interpolate_new(name)
+    if interpolate == nil then
+        error("no such interpolator\n" .. verror.get())
+    end
+
+    return Interpolate.new(interpolate)
+end
+
+return ffi.metatype("Interpolate", {
+    __index = Interpolate
+})
+
+
diff --git a/src/vips/cdefs.lua b/src/vips/cdefs.lua
index 81e427e..3ba723a 100644
--- a/src/vips/cdefs.lua
+++ b/src/vips/cdefs.lua
@@ -186,6 +186,8 @@ ffi.cdef [[
         // opaque
     } VipsOperation;
 
+    VipsInterpolate *vips_interpolate_new (const char *name);
+
     VipsOperation *vips_operation_new (const char *name);
 
     typedef void * (*VipsArgumentMapFn) (VipsOperation *object,